Presenting a live 90-minute webinar with interactive Q&A. Today s faculty features:

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1 Presenting a live 90-minute webinar with interactive Q&A Electronic Spying and Tracking Spouses in Divorce: Admissibility and Privacy Issues Navigating Evidentiary Issues With Spyware, GPS Trackers, Cell Phone Forensics, Wiretaps, Social Media and More TUESDAY, MAY 7, pm Eastern 12pm Central 11am Mountain 10am Pacific Today s faculty features: Henry S. Gornbein, Attorney, Henry S. Gornbein, Bloomfield Hills, Mich. Sharon D. Nelson, President, Sensei Enterprises, Fairfax, Va. John W. Simek, Vice President, Sensei Enterprises, Fairfax, Va. E.X. Martin, III, Law Offices of E.X. Martin, Dallas The audio portion of the conference may be accessed via the telephone or by using your computer's speakers. Please refer to the instructions ed to registrants for additional information. If you have any questions, please contact Customer Service at ext. 10.

2 Strafford Legal Webinars Cell Phone Forensics For Criminal Defense Attorneys & ipad For The Defense By E. X. Martin, III Attorney at Law 8828 Greenville Avenue Dallas, Texas Voice exmartin@airmail.net Introduction ipad & iphone For The Defense I am sixty six years old, married, and have one son. His name is Xerxes Martin, IV. Xerxes was an All State Pitcher in high school and later played baseball on the Baylor University Baseball team. He graduated from South Texas School of Law in May, 2011 and is now a practicing attorney in Dallas. Page - 1

3 I have learned a great deal about baseball and about people by watching my son's games and working with the players and coaches. His pitching coach, Mike Bacsik, gave me a book entitled The Mental Game of Baseball. At first, I thought this book would be dull and too sophisticated for me. I was wrong on both counts. It is more than a baseball book. Its focus and application relates to baseball but it also has suggestions that can be applied to the practice of law. I have been speaking to attorneys throughout the United States about using computer technology to increase their professional competence, to improve their productivity, and to help their clients with their legal problems. Chapter Eight of The Mental Game of Baseball contains these suggestions regarding learning that I think attorneys will find to be stimulating and inspiring especially with respect to using new technology in their law practices. Intentional Learning What to Want We want to look for better ways of doing "our thing" and have an open mind. We want to experiment with these new approaches. We never want to be satisfied with our knowledge or our skill. We want to recognize that new ways are not immediately comfortable. We want to give these new approaches a fair test of time - and effort. We want to think and talk about the solution, not the problem. We want to use our minds and control our emotions. We want to keep what works and discard what doesn't. We want to be persistent. We want to remember that mistakes are first steps to learning and should not be labeled as "failures." We want to remember that many people avoid learning new ways of doing things because, in addition to not wanting to feel uncomfortable, they "don't want to look bad." We want to remember that good learners "risk" doing things badly, in order to find out how to do things well. We want to remember that had we waited until we could have walked perfectly before we made our attempts, we never would have attempted. We want to recognize there is always a need to learn. Page - 2

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5 Part I Cell Phone Forensics For Criminal Defense Attorneys I read a marketing article recently which stated that there are more than 7 billion people on the planet. 5.1 billion of them own a cell phone, but only 4.2 billion own a toothbrush. Cell phone use has increased tremendously over the last decade. Additionally, the utility and capabilities of cell phones and / or smart phones has increased beyond almost anyone s expectations. I frequently refer to my cell phone as a phone with a computer wrapped around it that has much more ability than just making phone calls. I also tell young attorneys that all they need to start their law practice is a law degree and a smart phone. Today a smart phone can assist attorneys with calendar and contact management, marketing, legal research, credit card payment processing, document access and scanning, internet access, and texting, power point or key note presentations, remote access to another computer, internet document backup, file access and transferring through cloud computing, and photographic, video, and audio recording capability. While cell phones are both useful and helpful to ordinary people, unfortunately they are also used directly or indirectly in the commission of criminal offenses. Law enforcement uses technology to combat crime, just as criminals use it for their purposes. The widespread use of cell phones has resulted in the development of forensic extraction devices and their software that law enforcement can use to examine a suspect s mobile phone for incriminating evidence. Cell phones today hold immense amounts of personal information in which arrestees conceivably have significant privacy interests. Cell phones equipped with GPS navigation generate geo-locational information (GEO tags) that can be located and extracted to determine the location of the cell phone or even produce a location tracking map of specific cell phones. This information or evidence may also determine the types of activities a person engages Page - 4

6 in at a particular location. Most people do not realize that, when they move about or travel with a cell phone, they may well be creating a detailed record of their whereabouts. Law enforcement is well aware of value of geo-locational data with respect to criminal cases. Law enforcement can subpoena tracking records from cell phone companies when investigating a particular individual or criminal offense. An article in The New York Times on July 12, 2012, stated that cell phone carriers reported that they responded to a startling 1.3 million demands last year from law enforcement agencies for cell phone subscriber information seeking text messages, caller locations, and other information in the course of investigations. Furthermore, law enforcement officers are now routinely conducting forensic examinations or cell phone dumps on cell phones seized subsequent to an arrest or search. The evidence obtained from a person s cell phone can be used to corroborate evidence obtained from cell phone carriers or vice versa. Generally the examinations are conducted using the popular and powerful Cellebrite device shown below. The Cellebrite is a very advanced smart phone forensic analysis tool. It allows the user to extract call activity, contact lists, calendar information, voice mails, text messages, photographs, videos, software applications (apps), passwords, geo-locational data gained from cellphone towers, Wi-Fi hotspots, and more. The device can also download copies of an smart phone s existing, hidden, and deleted phone data, including call history, text messages, contacts, images, and geotags in a short time span. The Cellebrite device allows the user to conduct quick, easy phone searches and this device is wide acceptance with all law enforcement agencies. The Cellebrite s abilitythat makes it easy for law enforcement officers to conduct these intrusive cell phone searches is a hot button issue with the ACLU and other individual privacy watchdogs. Page - 5

7 Current Search Issues Regarding Cell Phones State Appellate Courts Are Split On Weather Search Of Cell Phone Requires A Warrant Supreme Court Of California It certainly appears to me that our state and federal courts are generally upholding searches of cell phones subsequent to an arrest with or without a warrant. On January 3, 2011, the Supreme Court of California in The People v. Gregory Diaz, 119 Cal.Rptr.3d 105, upheld a warrantless search of a cell phone that was taken from the defendant s person subsequent to his warrantless arrest for a felony drug offense. A text message retrieved from the cell phone s text message folder was consistent with the defendant having knowledge of drug transactions. The defense moved to suppress the fruits of the cell phone search the text message arguing that the warrantless search of the cell phone violated the Fourth Amendment. The trial court upheld the search and the case was ultimately appealed to the Supreme Court of California. The California Supreme Court relied on United States v. Robinson (1973), 414 U.S. 218, 94 S.Ct. 467, 38 L.Ed.2d 427, which established the exception to the Fourth Amendment s warrant requirement of a search incident to lawful arrest. This exception has traditionally been justified by the reasonableness of searching for weapons, instruments of escape, and evidence of crime when a person is taken into official custody and Page - 6

8 lawfully detained. The California Supreme Court cited United States v. Edwards (1974), 415 U.S. 800, 94 S.Ct. 1234, 39 L.Ed.2d 771, in which the high court explained: When a custodial arrest is made, there is always some danger that the person arrested may seek to use a weapon, or that evidence may be concealed or destroyed. To safeguard himself and others, and to prevent the loss of evidence, it has been held reasonable for the arresting officer to conduct a prompt, warrantless search of the arrestee s person and the area within his immediate control Such searches may be conducted without a warrant, and they may also be made whether or not there is probable cause to believe that the person arrested may have a weapon or is about to destroy evidence. The potential dangers lurking in all custodial arrests make warrantless searches of items within the immediate control area reasonable without requiring the arresting officer to calculate the probability that weapons or destructible evidence may be involved. See also: United States v. Chadwick (1977), 433 U.S. 1, 97 S.Ct. 2476, 53 L.Ed.2d 538. In conclusion, the majority of the California Supreme Court held that the police may, without obtaining a warrant, view or listen to information electronically stored on a cell phone that the defendant was carrying when lawfully arrested. Supreme Court Of Ohio The Supreme Court of Ohio in State v. Smith, 920 N.E.2d 949 decided December 15, 2009, was asked to determine whether the Fourth Amendment to the United States Constitution prohibits the warrantless search of data with a cell phone when the phone is lawfully seized incident to an arrest. The defense based his case on the Fourth Amendment to the United States Constitution, which provides protection against unreasonable searches and seizures and argued that it is well established that searches conducted without a warrant are per se unreasonable, subject to certain jealously and carefully drawn exceptions. The prosecution relied on the exception of a search incident to arrest, which allows officers to conduct a search that includes an arrestee s person and the area within the arrestee s immediate control. Chimel v. California (1969), 395 U.S. 752, , 89 S.Ct. 2034, 23 L.Ed This exception derives from interests in officer safety and evidence preservation that are typically implicated in arrest situations. Arizona v. Gant (2009), 556 U.S., 129 S.Ct. 1710, 1716, 173 L.Ed.2d 485. The prosecution also argued that the cell phone was analogous to a closed container that was found on the defendant s person and thus may be searched. See United States v. Finley (C.A.5, 2007), 477 F.3d 250. The prosecution further argued that the Ohio Supreme Court should follow Finley and affirm the conviction because the trial court was correct in its conclusion that a cell phone is akin to a closed container and thus subject to search subsequent to a lawful arrest. The Ohio Supreme Court did not agree with this comparison reasoning that objects following under the banner of closed container have traditionally been physical objects capable of holding other physical objects. Indeed, the United States Supreme Court has stated that in this situation, container means any object capable of holding another object. New York v. Belton (1981), 453 U.S. 454, 460, 101 S.Ct. 2860, 69 L.Ed.2d 768. The Ohio Supreme Court further noted the U.S. Supreme Court s definition of container in Belton, which implies that the container must actually have a physical object within it and thus held that a cell phone is not a closed container for purposes of a Fourth Amendment analysis. The Court further opined that modern understandings of the Fourth Amendment recognize that it serves to protect an individual s subjective expectation of privacy if that expectation is reasonable and justifiable. The Court held that the ability of cell phones to store large amounts of private data gives their users a reasonable and justifiable expectation of a higher level of privacy in the information they contain. Additionally, once the cell phone is in police custody, the state has satisfied its immediate interest in collecting and preserving evidence and can take preventive steps to ensure that the data found on the phone are neither lost nor erased. But because Page - 7

9 a person has a high expectation of privacy in a cell phone s contents, police must then obtain a warrant before intruding into the phone s contents. The Ohio Supreme Court concluded that the warrantless search of data within a cell phone seized incident to a lawful arrest is prohibited by the Fourth Amendment when the search is unnecessary for the safety of law-enforcement officers and there are no exigent circumstances, Furthermore, because the prosecution failed to show that either of these exceptions to the warrant requirement applied, the search of the defendant s cell phone was improper, and the trial court was required to exclude from evidence the call records and phone numbers taken from the cell phone. Additionally, various types of digital evidence (text messages, photographs, geo-locational data, etc.) extracted from cell phones is being used in the prosecution of criminal cases. For this reason it is important for criminal defense attorneys to be familiar with what can be obtained from a forensic examination of a cell phone by a Cellebrite or similar device. Law enforcement recognizes that cell phones hold enormous amounts of data and thus they have become attractive targets for their evidentiary value. Just as cell phones and smart phones have increased their processing power and utility, devices that are capable of forensically examining these devices have also become much more sophisticated. One such device is the Cellebrite UFED Touch. This device is made specifically to extract, decode, and analyze data from mobile devices. It performs physical, logical, file system and password extraction of all data (even if deleted) from smartphones, portable GPS devices, tablets and phones manufactured with Chinese chipsets. The Cellebrite allows law enforcement officials to crack suspects mobile phones in what is now called a cell phone dump and mine them for incriminating information. The Cellebrite also allows private forensic examiners to examine the data to find information that is helpful to the citizen accused. Page - 8

10 Part II Forensic Examinations Of Cell Phones Cellebrite UFED Touch Device Cellphone forensics is a branch of digital forensics relating to recovery of digital evidence or data from a mobile device under forensically sound conditions. It can also relate to any digital device that has both internal memory and communication ability, including PDA devices, GPS devices, thumb drive, and tablet computers. The use of phones in crime was widely recognized for some years, but the forensic study of mobile devices is a relatively new field, dating from the early 2000s. The widespread use of cellphones (particularly smartphones) on the consumer market caused a demand for forensic examination of the devices, which could not be met by existing computer forensics techniques. Today, smart phones can be used to save several types of personal information such as contacts, photos, calendars and notes, SMS and MMS messages. Smartphones may additionally contain video, , web browsing information, location information, and social networking messages and contacts. As mobile device technology advances, the amount and types of data that can be found on a mobile device is constantly increasing. Evidence that can be potentially recovered from a mobile phone may come from several different sources, including handset memory, SIM card, and attached memory cards such as SD cards. This data or information can have evidentiary value in a criminal case. Traditionally mobile phone forensics has been associated with recovering SMS and MMS messaging, as well as call logs, contact lists and phone IMEI/ESN information. However, newer generations of smartphones also include wider varieties of information; from web browsing, Wireless network settings, geolocation information (including geotags contained within image metadata), and other forms of rich internet media, including important data -- such as social networking service posts and contacts -- now retained on smartphone 'apps'. Page - 9

11 Data Acquisition Types Cellphone data extraction is commonly classified according to which extraction methods are more technical and forensically sound. The completeness of the cellphone data extraction can depend on the sophistication of the software used for the examination. A thoroughly sound forensic examination of a cellphone can be timely. Manual Analysis Of Cellphone Data The forensic examiner utilizes the cellphone s user interface to investigate the content of the phone's memory. Therefore the device is used as normal, with the examiner taking pictures of each screen's contents. This method has an advantage in that the operating system makes it unnecessary to use specialized tools or equipment to transform raw data into human interpretable information. In practice this method is applied to cell phones, PDAs and navigation systems. Disadvantages are that only data visible to the operating system can be recovered; that all data are only available in form of pictures; and the process itself is time-consuming. Logical Analysis Logical acquisition implies a bit-by-bit copy of logical storage objects (e.g., directories and files) that reside on a logical store (e.g., a file system partition). Logical acquisition has the advantage that system data structures are easier for a tool to extract and organize. Logical extraction acquires information from the device using the original equipment manufacturer application programming interface for synchronizing the phone's contents with a personal computer. A logical extraction is generally easier to work with as it does not produce a large binary blob. However, a skilled forensic examiner will be able to extract far more information from a physical extraction. Physical Analysis Physical acquisition implies a bit-for-bit copy of an entire physical store (e.g. flash memory); therefore, it is the method most similar to the examination of a personal computer. A physical acquisition has the advantage of allowing deleted files and data remnants to be examined. Physical extraction acquires information from the device by direct access to the flash memories. Generally this is harder to achieve because the device original equipment manufacturer needs to secure against arbitrary reading of memory; therefore, a device may be locked to a certain operator. To get around this security, mobile forensics tool vendors often develop their own boot loaders, enabling the forensic tool to access the memory (and often, also to bypass user passcodes or pattern locks). Generally the physical extraction is split into two steps, the dumping phase and the decoding phase. A physical analysis may well allow the recovery of additional evidence. I recently participated in a case where the law enforcement agency did a logical analysis of the seized smartphone. I had my forensic expert conduct a Physical Analysis and we recovered additional evidence including: 1. 15, 000 additional images additional videos audio files 4. 12,000+ locations MMS messages Page - 10

12 text files I have worked with friend and computer expert, Lance Sloves, on several cases involving electronically stored information that has been obtained from a defendant s smart phone. Recently I had Lance do a cell phone dump of my iphone 5 for this paper and I was able to make some computer screen snap shots which I believe demonstrate the Cellebrite s extraction and analyzing capabilities. I am reproducing the screen snap shots that I made because I believe they will be helpful to the defense bar in understanding what can be obtained by the Cellebrite device. The photographs below show the Cellebrite kit containing various cables and connectors than can be used to extract data and information from a variety of mobile devices including older legacy phones and smartphones such as the iphone, Android, BlackBerry, Nokia, Windows Mobile, and Palm. Page - 11

13 The next photograph shows the iphone 5 connected to the Cellebrite UFED Touch at the start of the cell phone dump of this device. The following photograph is of the desktop computer that was used in conjunction with the Cellebrite device during the examination of the iphone 5 in this particular example. The Cellebrite is connected to a desktop or laptop computer using a USB cable to transfer the extracted data. The Cellebrite Physical Analyzer software runs on the desktop computer and will expose every segment of a device s memory data and export this data into an easy to use software program that helps one organize, analyze, and understand the extracted data and information. The following screen snapshots were taken from the monitor of this computer and are reproduced here to help one understand the extraction process and also how the extracted data is organized in a manner that helps you drill down to, organize, and understand the information that is important to your client in a particular case. Page - 12

14 The following graphic image is the Cellebrite Physical Analyzer & Extraction Summary window. Well Formatted Report The previous graphic should give you a pretty good idea of the type of information that you can extract from a smart phone. The column on the left side of the graphic under the Analyzed Data tab lists Bluetooth Devices, Calendar, Call Log, Chats, s, Installed Applications, IP Connections, Locations (10,344), Maps, Passwords, Searched Items, SMS Messages, User Accounts, Wireless Networks (44). Under Data files you have images (47,8007), Videos (48), Audio (911), Text (713), Databases, Configurations, and Applications. At the bottom of the previous graphic and the cut out graphic below you can see the icon buttons that can be used to access specific data by touching the icon. Page - 13

15 I find this next graphic image particularly interesting. It is an extraction summary of calls made from the iphone and received in both spreadsheet format and graphically. The spreadsheet highlights calls to and from and missed from my friend Justice Jim Moseley. Seven calls are listed and bar graph shows one incoming call, four outgoing, and two missed calls. You can also see the list of phone numbers, related name, total for each individual both incoming, outgoing, and missed. It is easy to see how helpful this information could be in a particular case. The following graphic displays various text messages received on the iphone. I consider this image particularly important because text messages are being used is some manner in trial in almost every criminal case. This graphic should give you some idea of how a forensic exam of a cell phone could help you find the text message you need and pinpoint it as to time and place. Page - 14

16 This next graphic image pertains to location information gathered from various sources such as cell towers, media locations which can be photographs with embedded geo-locational information, and Wifi networks. When I was reviewing some of the data pertaining to the iphone 5 accessing wireless networks, I notice that one wireless connection was from the Westin Beach Resort in Fort Lauderdale, Florida. On February 17, 2012, I spoke at an NACDL seminar in Fort Lauderdale and stayed at the Westin Beach Resort and had in fact accessed the hotel s wireless network with the iphone. The extracted data confirmed my presence or at least the presence of my specific phone at the Westin Beach Resort in Fort Lauderdale. It is easy to say how such information could be used to prove a point in a trial. It is possible to export this data into a KML file that can then be opened in Google maps. It is easy to see how helpful this type of evidence could be if you are trying to show the tracking of an individual or a mobile device. Page - 15

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18 Part III How A Cellular Network Operates A cellular network or mobile network is a radio network distributed over land areas called cells, each served by at least one fixed-location transceiver, known as a cell site or base station. In a cellular network, each cell uses a different set of frequencies from neighboring cells, to avoid interference and provide guaranteed bandwidth within each cell. When joined together these cells provide radio coverage over a wide geographic area. This enables a large number of portable transceivers (e.g., mobile phones, pagers, etc.) to communicate with each other and with fixed transceivers and telephones anywhere in the network, via base stations, even if some of the transceivers are moving through more than one cell during transmission. Cellular Site Data Evidence Offered In A Criminal Case To Track The Location Of A Cellular Phone Prosecutors are increasing using cellular site data obtained from cellular service providers to corroborate other evidence placing the defendant at or near the crime scene. The law enforcement agents and prosecutors are subpoenaing a defendant s cell phone records relating to the date and time of the alleged offense. Cell Service Provider Business Records The prosecution will probably begin by moving to admit into evidence at trial the cell phone service provider call data records under the business record exception to the hearsay rule as provided in Fed. R. Evid. 803(6). A properly introduced, authenticated business record that meets the standards of the Federal Rules of Evidence ordinarily is nontestimonial and will not violate the Confrontation Clause. Assuming the proper foundation is laid, these records are likely admissible. See United States v. Graham, 846 F. Supp. 2d 384, 389 Page - 17

19 (D.Md. 2012) which stated that historical cell site location records are created by cellular providers in the ordinary course of business. When a cell phone is in idle mode, it regularly communicates with cell towers in its network. Using radio frequency waves, the phone tries to determine which cell tower has the strongest signal. In urban areas, cell towers are often located on top of buildings or water towers. A cell tower emits radio frequency waves in all directions, providing cell phone coverage in a 360 degree radius around the tower. Three antennas typically comprise each tower; each antenna covers a 120 degree area. When a cell phone places a call, it typically connects to the tower in its network with the strongest signal. This is usually the tower nearest to the phone, although a variety of factors including physical obstructions and topography can determine which tower services a particular phone. Once the call reaches the tower, this interaction is recorded by the network provider. The call then proceeds to a mobile switching center, which may choose to reroute the call to a different tower based on network traffic. The call may also be rerouted to a different tower if the caller changes location during the duration of the call. These data are recorded by the network and maintained as call data records. To determine the location of a cell phone, law enforcements agents or their experts generally identify (1) the physical location of the cell sites used by the phone during the relevant time period; (2) the specific antenna used at each cell site; and (3) the direction of the antenna s coverage. Then they estimate the range of each antenna s coverage based on the proximity of the tower to other towers in the area. This is the area in which the cell phone could connect with the tower given the angle of the antenna and the strength of its signal. They try and determine where the coverage area of one tower will overlap with the coverage of another. These facts are then used to estimate then general location of a cell phone within a specific time period. Admissibility Of Testimony Concerning How Cellular Networks Operate Whenever a person makes a call with a cell phone, the call routed through a cell tower located at a fixed geographic location. Cell service providers keep records of which cell tower processed a call. This is the information that prosecutors attempt to use the establish the location of the cell phone and its user. It is easy to see and understand how this type of evidence can be used by the prosecution to place the defendant at the place and time of the offense charged. The accuracy and precision of this evidence varies on a case by case basis. Generally the admission of this type of evidence interpreting cell site geolocational data requires expert testimony. However, some courts have allowed law enforcement officers to provide lay opinion testimony as to Page - 18

20 how cellular networks operate or the use of call data records to determine the location of a cell phone. United States v. Feliciano, 300 F.App x 795, 801 (11 th Cir. 2008). The defense should request a hearing under Federal Rule of Evidence 702 and Daubert to determine whether the prosecution s proposed evidence and analysis are admissible. The prosecution must show that their expert is qualified to testify about how cellular networks operate and the accuracy of geolocational data offered to link the accused to the crime. Legal Standard The admission of lay witness testimony is governed by Federal Rule of Evidence 701, which limits lay opinion testimony to that which is (1) rationally based on the witness s perception; (2) helpful to clearly understanding the witness s testimony or to determining a fact in issue; and (3) not based on scientific, technical, or other specialized knowledge within the scope of Rule 702. Fed. R. Evid The admission of expert opinion testimony is governed by Federal Rule of Evidence 702 and Daubert. See Bielskis v. Louisville Ladder, Inc., 663 F.3d 887, 893 (7th Cir. 2011). Rule 702 states that a witness who is qualified as an expert by knowledge, skill experience, training or education may testify in the form of opinion or otherwise provided that (1) the expert s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue; (2) the testimony is based on sufficient facts or data; (3) the testimony is the product of reliable principles and methods; and (4) the expert has reliably applied the principles and methods to the facts of the case. Fed. R.Evid To admit expert testimony under this rule, the court must determine that (1) the witness is qualified; (2) the expert s methodology is scientifically reliable; and (3) the testimony will assist the trier of fact to understand the evidence or to determine a fact in issue. Myers v. Ill. Cent. R.R. Co., 629 F.3d 639, 644 (7th Cir. 2010). In Daubert the United States Supreme Court set out four factors the court may consider when assessing the reliability of an expert s methodology, including (1) whether the theory is based on scientific or other specialized knowledge that has been or can be tested; (2) whether the theory has been subjected to peer review; (3) the known or potential rate of error and the existence of standards controlling the theory s operation; and (4) the extent to which the theory is generally accepted in the relevant community. Daubert, 509 U.S. at ; see also Kumho Tire Co. v. Carmichael, 526 U.S. 137, 151, 119 S. Ct. 1167, 143 L. Ed. 2d 238 (1999). The Rule 702 inquiry is a flexible one. Daubert, 509 U.S. at 594. As such, [d]eterminations on admissibility should not supplant the adversarial process; shaky expert testimony may be admissible, assailable by its opponents through cross-examination. Gayton v. McCoy, 593 F.3d 610, 616 (7th Cir. 2010). The proponent of the testimony bears the burden of proving that the proffered testimony meets these requirements, and the Seventh Circuit grants the district court wide latitude in performing its gate-keeping function. Bielskis, 663 F.3d at 894 (internal quotation marks and citation omitted). Page - 19