Admissibility of Historical Cell Site Data Analysis
Increasingly, prosecutors have been attempting to use the location of cell phones as evidence against defendants. While there are no published opinions in New Jersey squarely addressing the admissibility of cell site data analysis in a criminal case, unpublished opinions have generally held that historical cell site data analysis is generally acceptable in the scientific community and reliable. One such case is State v. Carrera, a 2019 New Jersey Appellate Division opinion. After an extensive hearing, the court described the cell site analysis evidence as follows.
From the moment a cell phone is turned on it constantly scans the radio frequency environment for the strongest cell tower signal. The cell phone’s scanning takes place whether or not the cell phone is moving. When a cell phone sees a tower, it identifies itself, provides its location to the tower, and receives acknowledgment from the tower. The tower with the strongest, clearest signal is the one to which the cell phone will most likely connect. This is known as the “serving cell” and is not necessarily the closest in proximity to the cell phone, as the closest tower may not be operative, or its signal may be blocked by an obstruction, such as a building or natural landscape feature. The cell phone checks other towers in the area and measures the signal strength of those towers. If a cell phone is in an area of overlapping coverage, it may switch back and forth between serving cells whether located on a tower or other structure.
A cell phone can communicate with a tower only if the cell phone is within the tower’s range. An at-capacity or full tower, therefore, will never reroute a cell phone to a tower to which the cell phone cannot connect.
A record is generated when a cell phone connects to a tower to make a call. The record contains the calling number, the number dialed, the date and time that call was placed, the end time of the call, the duration of the call, and the last tower to which the phone was connected during the call. An ongoing call may be transferred from tower to tower, particularly if the cell phone is moving, but may also be transferred when a tower approaches capacity. Only the towers at which a call originates and ends are recorded.
Historical cell site data analysis provides “the approximate area... of where a cell phone was when it connected” to an identified sector of a tower at a particular date and time. A typical cell tower has three 120 degree sectors, covering the full 360 degrees surrounding the tower with antennae tilted downward for the purpose of providing blanket connectivity near the tower.
Expert testimony is limited. All an expert can state is, the phone utilized a particular tower and a particular sector and that the sector most likely covers a particular area. There is no way to determine how far away a phone was with from a particular tower and expert analysis would never be able to precisely locate a phone, for example at a street address. Terrain, buildings, glass structures, concrete, a bus, water and even a creek bed can affect whether a cell phone connects to the geographically closest cell tower or another one.
It is undisputed that a tower’s footprint can shift over time due to changes in the surrounding environment. “Because radio waves extend out horizontally and then descend, coverage is affected by the surrounding topography . . . .” Sprint Spectrum, L.P., 360 N.J. Super. 373, 379 (App. Div. 2003). While the proximity of the user is a significant factor in determining the cell tower with which the cell phone connects, it is not the only one. . . . Other factors include, geography and topography . . . and environmental and geographical factors.
Federal courts have been receptive to expert testimony regarding historical cell site data analysis. “District courts that have been called upon to decide whether to admit historical cell-site analysis have almost universally done so.” United States v. Hill, 818 F.3d 289, 297 (7th Cir. 2016); United States v. Weathers, 169 F.3d 336, 339 (6th Cir. 1999) (admitting expert testimony on historical cell site data analysis); United States v. Jones, 918 F. Supp. 2d 1, 5 (D.D.C. 2013) (finding “the use of cell phone location of a cell phone” to be both widely accepted and “based on reliable methodology”).
In addition, most States Courts have upheld its admissibility. State v. DePaula, 166 A.3d 1085, 1097-99 (N.H. 2017) (admitting historical cell site data analysis as lay witness testimony); State v, Johnson, 797 S.E.2d 557, 563 (W.Va. 2017); Pullin v. State, 534 S.E.2d 69,71 (Ga. 2000); Wilson v. State, 195 S.W.3d 193, 200-02 (Tex. Crim. App. 2006) (allowing a Sprint employee to testify as an expert on historical cell site data analysis); contra Phillips v. State, 163 A.3d 230, 234 (Md. Ct. App. 2017).
Courts, however, have barred admission of expert testimony on historical cell site data analysis where the method used by a particular expert renders the testimony unreliable. See generally Omnipoint Commc’n Enters., L.P. v. Zoning Hearing Bd., 331 F.3d 386, 399 (3rd Cir. 2003)(finding a lack of drive test data renders an expert’s opinion on signal strength unsupported).
New Jersey has allowed expert testimony on drive testing in civil matters for the purpose of showing lackluster cell coverage in a municipality. N.Y. SMSA Ltd. v. Twp. of Mendham Zoning Bd. Of Adjustment, 366 N.J. Super. 141, 150 (App. Div. 2004). A test drive consists of the expert using a phone or other mobile devices to confirm the cell site data analysis. In State v. Carrera, the court disallowed expert testimony because the test drive was conducted over 2 years after the crime in question. The court noted that buildings could have been constructed or demolished in this time period which would effect the cell tower that a cell phone would connect to. In other words, a new building could affect which tower was utilized by a cell phone.
In conclusion, the cell site data analysis generally will be admitted into evidence, but it should be carefully reviewed and an independent expert consulted. In addition, if a test drive was not conducted, the cell site testimony could be barred from the trial.