The Promise & Peril of CDRs – Misleading the Jury

Modern cell towers generate complex datasets that require expert interpretation in court.

What Are CDRs, and What Do They Really Show?

Call Detail Records are logs maintained by wireless carriers, documenting calls, texts, and data sessions, along with the cell towers and sectors involved. A single case may involve thousands - or even hundreds of thousands - of such records, each a snapshot of a device’s interaction with the network.

When properly analyzed, CDRs can reveal:

• Tower Connections: Which cell tower a device connected to during a call, text, or data session.
• Activity Patterns: The frequency and timing of connections, showing communication trends.
• Phone Associations: Links between phone numbers and specific activities.

However, CDRs records alone cannot typically provide precise, GPS-level location data. At best, they indicate a device’s general proximity to a tower, often within a radius of several miles. These records alone do not generally pinpoint a person’s exact location, such as where they were standing at a given moment.

A common issue in court is the selective presentation of evidence. Prosecutors may highlight records that fit their narrative while ignoring thousands of others that could contradict it. For defense attorneys, the opportunity lies in scrutinizing these overlooked records to uncover inconsistencies or exculpatory evidence.

Preservation is critical. At the outset of a case, defense teams should issue preservation letters and sealed ex parte orders to ensure carriers retain original records. Delayed action risks the loss of critical data, as carriers may purge records after a set period.

Debunking the “Closest Tower” Myth

A pervasive courtroom myth is that a phone always connects to the nearest cell tower. This assumption is often incorrect and can lead to flawed conclusions. Cell towers typically cover a circular area with a radius of a few miles, but coverage varies based on multiple factors.

In reality, phones connect to the tower with the strongest signal, not necessarily the closest one. Several variables influence this connection:

• Network Load: During peak usage times, a phone may be routed to a less congested, more distant tower.
• Obstructions: Buildings, hills, trees, or even weather conditions can weaken signals from nearby towers.
• Interference: Competing radio frequencies can disrupt connections, pushing a phone to an alternative tower.
• Multipath Propagation & Rayleigh Fading: Signals can bounce off surfaces or overlap, causing unpredictable connections.

This means two phones in the same location could connect to different towers simultaneously, undermining assumptions about a defendant’s whereabouts.

For defense attorneys, challenging the “closest tower” myth is critical. Just because a client’s phone connected to a tower near a crime scene does not mean they were within close proximity to the tower.

Multipath propagation: phones often connect to the strongest available signal, not the nearest tower.

Some carriers provide enhanced datasets like NELOS, RTT, PCMD, or TDOA, marketed as “precision” location tools. However, carriers themselves caution that these are:

• “Best estimates”, not definitive locations.
• Not equivalent to historical GPS data.
• To be used with caution due to inherent inaccuracies.

Despite these disclaimers, law enforcement and prosecutors often present such data as precise and irrefutable. In truth, no historical CDR can pinpoint a phone’s exact geographic location, and the methodologies used to collect and analyze this data lack validated error rates.

Per Call Measurement Data (PCMD) and Timing Advance

PCMD relies on a process called Timing Advance, which functions similar to sonar. The carrier measures how long it takes for a signal to travel from the handset to the tower and back. Because the speed of radio waves is known, the system can calculate how far the phone is from the tower.

This sounds precise, but the limitation is critical: signals radiate outward in arcs within a tower’s sector. That means the phone could be located anywhere within a 10-meter-wide arc inside the tower’s azimuth, not at a fixed point. In practice, this leaves a band of possible locations rather than an exact GPS coordinate.

Time Difference of Arrival (TDOA) and Enhanced 911

T-Mobile employs Time Difference of Arrival (TDOA) in its Enhanced 911 (E911) services, using signals received at three or more antennas to triangulate a handset’s location. This can improve accuracy but is still dependent on network conditions, timing synchronization, and geography.

Carrier-Specific Systems

• AT&T – NELOS: The Network Event Location System relies on timing advance. AT&T has historically relied on NELOS but is transitioning toward a TDOA-based PCMD model similar to T-Mobile’s.
• Verizon – RTT: Range to Tower uses a variation of timing advance. Like NELOS and PCMD, RTT offers estimates but is not derived from GPS.
• T-Mobile – PCMD (“TrueCall”): Once branded as TrueCall, T-Mobile’s PCMD records use TDOA methodology for E911 services.

The “Historical GPS” Misconception

These datasets are sometimes mischaracterized by law enforcement as “historical GPS.” That is inaccurate. None of these methods use the phone’s onboard GPS radio; instead, they rely on network timing estimates - and those estimates can be imprecise.

Yet juries often overestimate this evidence, treating it as objective forensic science when it is anything but. Defense attorneys should challenge such evidence under Federal Rules of Evidence 702, 901, and 403, emphasizing the lack of validation, the disclaimers from carriers, and the risk of misleading jurors. At a minimum, raising these challenges preserves issues for appeal.

The Dangers of Automated Analysis

Automated software tools can generate visually compelling maps and reports from CDRs, but they are not a substitute for scientific rigor. In Denmark, flawed automated analysis led to a major scandal, with software errors linking phones to towers hundreds of miles away. This prompted the review of over 10,000 verdicts and a temporary ban on cell tower evidence.

Consider an analogy: many attorneys use QuickBooks for accounting, but this doesn’t make them certified accountants. Similarly, CDR software is a tool, not a replacement for expert interpretation. Automated outputs can oversimplify complex data, leading to erroneous conclusions.

At Black Dog Forensics, we emphasize human expertise over automation, ensuring that every record is meticulously reviewed for accuracy and context.

Validating CDRs with Drive Testing and Record Review

To counter misleading CDR evidence, defense teams must validate the data through:

Cell Site Surveys & Drive Testing

Drive testing involves traveling through the relevant area with specialized radio frequency equipment to measure actual signal strength, tower coverage, and handoff behavior. This process reveals how a phone would realistically connect to towers under similar conditions (assuming that’s even possible), exposing gaps or contradictions in the state’s claims.

Courts have acknowledged that historical mapping alone can be unreliable. Mapping has varying levels of accuracy and can provide an unreliable interpretation of the actual evidence.

Comprehensive Record Review

Every CDR dataset contains thousands of entries. With so much data, anomalies are inevitable. Too often, law enforcement highlights only the anomalies that support their narrative while ignoring those that favor the defense. A comprehensive review - examining all records, not just those cherry-picked by the prosecution - can uncover exculpatory patterns, alternative explanations, or inconsistencies that weaken the state’s theory.

Why Validation Matters

Without validation, CDR evidence risks being little more than a set of assumptions dressed up as science. By combining real-world drive testing with a full-scope record review, defense attorneys can:

• Demonstrate when a tower connection likely would not have occurred as claimed.
• Show that the same phone could connect to multiple towers from the same location. This is typically demonstrated by seeding the network with a handset of the exact make and model, using controlled test datasets that include both dedicated short calls and dedicated long calls.
• Highlight alternative data points that undercut the prosecution’s timeline.

Our goal is simple: to turn speculative tower evidence into reliable, court-ready truth. Where prosecutors may offer assumptions, we provide verified facts. Where maps and charts may mislead, we deliver clarity that judges and juries can trust. At Black Dog Forensics, our mission is to replace uncertainty with confidence and ensure that digital evidence serves justice - not speculation.

Beyond CDRs: Leveraging Other Location Data

CDRs are just one piece of the location evidence puzzle. Combining them with other sources of data can strengthen a defense case or expose weaknesses in the prosecution’s narrative. Additional sources include:

• Device Extractions: iOS/Android location history, such as Apple’s “Significant Locations” or Google Timeline.
• Cloud Data: Location records from iCloud, Snapchat, or other apps.
• Vehicle GPS & Telematics: Data from in-car navigation or tracking systems.
• DVR & Video Footage: Surveillance from stores, traffic cameras, or other locations can verify a defendant’s presence and be cross-checked against cell tower records to confirm - or challenge - the prosecution’s claims.

Requesting and investigating these records early - ideally through a sealed ex parte order - allows the defense to analyze potential exculpatory evidence before the prosecution shapes its narrative. Black Dog Forensics assists attorneys in drafting precise subpoena language to secure these records efficiently. We guide you on exactly who to ask, and what to ask for.

Turning Raw Records into Reliable Evidence

Cell tower records are powerful but prone to misinterpretation. Without expert context, they can mislead judges and juries. Simply put, cellphone location evidence has been offered as accurate by law enforcement and accepted as accurate by courts without any validation or proven reliability.

At Black Dog Forensics, our mission is truth-first digital forensics. We validate, test, and present evidence in a way that courts can trust, helping defense attorneys challenge junk science and protect their clients’ rights. We take it a step further by helping prepare in-depth lines of questioning to use against the state’s witness.

By exposing gaps, assumptions, and limitations in the state’s analysis, we help defense teams shift the narrative from “certainty” to “reasonable doubt.”

For expert CDR analysis and cell tower evidence interpretation, visit Black Dog Forensics or contact us to discuss your case.

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