A mast on a map: what cell-site evidence can really establish

Public record

The documented case and its important limits

In Carpenter v. United States, the US Supreme Court considered historical cell-site location information obtained from wireless carriers during a robbery investigation. Its opinion records that an expert used the data to map Carpenter's phone near four charged robberies. On 22 June 2018, the Court held that acquisition of the records at issue was a Fourth Amendment search, reversed the appellate judgment and remanded. The decision concerned constitutional protection, not a finding that the location analysis was scientifically defective. [1]

The procedural sequel matters: on 11 June 2019, the Sixth Circuit applied the good-faith exception because agents had reasonably relied on the Stored Communications Act, and affirmed the district court's judgment. The Supreme Court decision should therefore not be described as an acquittal or automatic exclusion of the records. [2]

365 ALTERAM analysis

The forensic question: what does this map represent?

A map can make an inference look like a measurement. A marker identifying a mast is not necessarily a marker locating the handset. Our independent-review question is whether the underlying record and method support the geographical claim being made, at the level of precision that matters to the allegation.

Three issues need separate treatment: what network event was recorded, what location inference it supports, and what evidence identifies the device's user. Reliable carrier data may still support a broader geographical conclusion than the prosecution narrative suggests. Equally, well-supported location evidence may materially strengthen an allegation.

Public record

A technical reference, with a defined jurisdiction

The Forensic Science Regulator's Code of Practice version 2 applies in England and Wales. Section 99 describes uncertainty in cell-site analysis, including network changes and differences between survey conditions and the historical event. It warns against pinpointing a device through ordinary cell-site analysis, while recognising that particular infrastructure, such as an indoor cell, may permit a more precise assessment. It also addresses the risk of wrongly excluding a possible location. These are jurisdiction-specific requirements, not a retrospective assessment of the Carpenter evidence. [3]

365 ALTERAM analysis

Reconstruct the event before drawing the route

Our proposed workstream begins with the provider disclosure, its field definitions and the relevant network information. Establish which identifier refers to the subscriber, SIM, handset, cell or sector. Check whether times describe the beginning or end of a call, or another recorded event, and document any conversion between time zones.

Preserve the supplied files and record every transformation used to produce the chronology or map. Request clarification through authorised channels where a field is ambiguous. A polished graphic should be reproducible from its source records, with missing information visible rather than concealed by presentation choices. In particular, explain whether lines joining recorded events merely aid reading or represent a route independently supported by evidence.

365 ALTERAM analysis

Test the proposed location and meaningful alternatives

A suitably qualified telecommunications specialist should assess the network configuration relevant to the historical event and the basis for any coverage interpretation. A later survey requires an explanation of its comparability. Ask whether the material supports presence within a service area, exclusion of a location, or a narrower conclusion supported by additional measurements.

A clearly labelled hypothetical illustrates the distinction: if a service area includes both a warehouse and surrounding roads, compatibility with the warehouse does not alone distinguish those locations. Independent CCTV, device records or other properly assessed evidence may help. The same discipline applies to an alibi: failure to detect a cell during a later survey does not automatically prove that it could not have served the location earlier.

365 ALTERAM analysis

Make the conclusion useful to the defence team

Counsel should receive an event chronology, an explanation of the identifiers and processing steps, maps with clearly stated assumptions, and a schedule of conclusions and limitations. Distinguish technical compatibility from evidence of actual presence. Where relevant, assess user attribution separately through lawfully available records. Report findings that support the allegation alongside those that weaken it, and identify questions the available material cannot resolve.

365 ALTERAM supports defence lawyers and accused persons in complex international cases through independent forensic telecommunications review and counter-investigation. Early review can focus disclosure requests and specialist examination before trial. Qualified counsel directs jurisdiction-specific legal strategy; no investigative or litigation outcome is guaranteed. To discuss the scope of a review, contact contact@365alteram.com. Before You Trust the File, Test It.