Written by Jarrett Ambeau, trial attorney, court-qualified expert in forensic DNA interpretation, and holder of a Master of Science in forensic DNA and serology, at The Ambeau Law Firm.
A cell tower is not a GPS pin.
The state loves to tell juries the phone “was at the scene.” Cell-site location data almost never proves that. It shows which tower a phone connected to, not where the phone stood. Those are very different facts, and the gap between them can decide a case.
Let’s say Cathy is accused of being at a robbery across town. The state maps her phone to a nearby tower and rests. But a tower can cover several square miles. Cathy could have been home the whole time. The map looks precise. It is not.
This evidence is powerful because it looks like technology cannot lie. A colored map with a neat circle feels like proof. The defense job is to show the jury how much guesswork hides behind that clean image.
What is cell-site location information?
Cell-site location information, or CSLI, is a record of which cell towers a phone used during calls, texts, and data sessions. The carrier logs the tower and often the sector, a wedge of the tower’s coverage area.
Here is the key point. A phone does not always connect to the closest tower. It connects to the tower with the best signal. Traffic load, weather, buildings, and terrain all push a phone to a tower that is not the nearest one. So the record tells you the network’s choice, not the person’s location.
There are two kinds of records, and they are not equal. Historical CSLI is the carrier’s stored billing data, built to bill customers, not to track movement. Real-time or per-call detail can be more granular, but still reflects coverage, not coordinates. The state often blurs the two. We do not let it.
The science: how phones actually pick towers
A cellular network is a web of overlapping coverage. Each tower reaches out in sectors, and those sectors overlap with neighbors. In a city, a phone may “see” a dozen towers at once and choose among them based on signal strength and network load.
Load balancing matters more than distance. When a nearby tower is busy, the network can route a phone to a farther tower with spare capacity. A big event, a traffic jam, or a shift change can all move where a phone connects. The record captures that routing decision, not a footstep.
Terrain and buildings bend the signal. A hill, a metal roof, or a river valley can block the closest tower and favor one miles away. The honest scientific picture is a broad, shifting probability zone, not a dot. Anyone who draws a dot is overselling the data.
Why cell-site testimony misleads juries
The danger is false precision. An analyst draws a tight circle on a map and the jury sees certainty. But the honest picture is a broad, overlapping coverage area, sometimes miles wide, that shifts by the hour.
The visual does the damage. A jury remembers the map, not the caveats. When the state’s witness says “consistent with being in this area,” the jury hears “he was there.” Those are not the same statement, and the difference is often reasonable doubt.
The law: privacy, admissibility, and reliability
First comes the Fourth Amendment. In Carpenter v. United States, 138 S. Ct. 2206 (2018), the Supreme Court held that the government generally needs a warrant to obtain historical cell-site records. If the state gathered your location history without a proper warrant, we move to suppress it.
Second comes reliability. When an analyst offers an opinion about where a phone was, that is expert testimony. Louisiana screens expert testimony under Code of Evidence Article 702 and the standard adopted in State v. Foret, 628 So.2d 1116 (La. 1993), which brought the Daubert v. Merrell Dow, 509 U.S. 579 (1993) factors into our courts. A “map” opinion that treats coverage as location can be challenged as unreliable under that framework.
Third comes the witness. Records do not authenticate themselves. The state needs a witness who understands the network to explain what the data means and, just as important, what it does not mean. We use cross-examination to force that witness to concede the limits.
How we challenge cell-site evidence: law and science together
We demand the raw records and the tower data behind the map, not just the state’s polished exhibit. We test whether the analyst confused coverage area with pinpoint location. That single error appears again and again.
On the law, we litigate the warrant under Carpenter, and we challenge the analyst’s opinion under the Foret and Daubert standard. If the method treats an overlapping, shifting coverage web as a fixed point, it fails the reliability test, and we say so in a motion before trial.
On the science, we bring in radio-frequency engineers who understand how networks actually route calls. When needed, they run a drive test, measuring real signal coverage in the area to show the true range. The real coverage map often destroys the state’s tidy circle.
At trial, we make the state’s witness draw the honest map. Not the marketing map, the real one, with the miles-wide coverage and the overlapping sectors. Once the jury sees how wide the zone really is, “he was at the scene” collapses into “he was somewhere in a large part of the city.”
Which cases turn on location data?
Cell-site data shows up in the highest-stakes cases. Homicide and armed-robbery prosecutions where the whole theory is that the defendant was present. Drug conspiracy cases that try to link people through movement. These are the serious felony charges where a shaky location map can mean the difference between a conviction and an acquittal.
The same data drives federal prosecutions, where investigators map a person’s movements over months. The longer the timeline, the more the science has to be tested, because small errors compound across every data point.
Frequently asked questions
Doesn’t the phone connect to the nearest tower?
Not always. Phones connect to the strongest available signal. Load, terrain, and buildings can route a phone to a tower that is not the closest one.
Can cell data really place me at a crime scene?
Rarely with precision. It shows a broad coverage area, not an exact spot. A careful defense exposes how wide that area really is.
Can the location records be suppressed?
Possibly. Under Carpenter v. United States, the government generally needs a warrant for historical cell-site data. A records grab without one can be challenged.
Do you use outside experts for this?
Yes. We work with radio-frequency engineers who can analyze the network data and, when useful, test the actual coverage on the ground.
Authoritative resources
The limits of this evidence are well documented. The Supreme Court examined how revealing and imperfect cell-site records are in Carpenter v. United States.
Related forensic evidence challenges
Forensic evidence rarely stands alone. We challenge the full range of scientific proof the state uses, including digital forensics and phone extractions, firearms and toolmark analysis, and fingerprint and latent print analysis. For the full picture, see our overview of what a forensic science lawyer does.
How The Ambeau Law Firm can help
If the state is using a map to put you at a scene, that map can be challenged. We litigate the warrant, test the data, expose the false precision, and make the analyst admit what the records cannot show. Contact The Ambeau Law Firm to discuss your case.