Wednesday, September 28, 2022

Crime Fiction Enters the Sensorvault Era: Guest Post by Chuck Greaves


The science of fingerprinting was pioneered by Sir Francis Galton, a British anthropologist who, beginning in 1888, published a series of monographs establishing that each individual’s prints are unique and that they remain so, unchanged, over a lifetime. Recognizing the significance of Galton’s research, Scotland Yard began collecting and compiling the fingerprints of arrestees for use in criminal investigations and prosecutions, and by the dawn of the twentieth century fingerprinting had become commonplace, both in policing and in the public’s understanding of police procedure.

Roughly a century after Galton’s pioneering research, DNA evidence was first employed in a rape and double-murder investigation in Leicester, England in 1986, both to exonerate the 17-year-old suspect already in custody, and later to identify and convict the actual killer. Subsequent advances in the extraordinary, revolutionary field of forensic genetics have allowed crime-scene investigators to extract and analyze genetic material from even the slightest biological trace evidence, and thereby to identify or exclude suspects using what amounts to their individual “genetic bar-codes.”

Today, perpetrators know better than to leave their fingerprints or their DNA at the scene of a crime, and crime writers know to use or manipulate such evidence in our stories. Thus our fictional burglars wear gloves, and our fictional killers wipe prints from their murder weapons, and our fictional CSI investigators probe and comb for minute bits of hair and blood evidence.

To simply ignore fingerprint or DNA evidence in our fiction would be to commit authorial malpractice. Yet that is precisely what many crime writers are doing when it comes to one of the latest and potentially most consequential items in the modern law enforcement tool box.

In October of 2021, I spoke at a crime convention in Crested Butte, Colorado and asked a roomful of veteran and aspiring mystery writers if they’d ever heard of Sensorvault. Not a single hand went up. Which didn’t surprise me, given the number of novels I’d been reading in which, had Sensorvault been employed, the story would have ended at around page 10.

Sensorvault was born in 2009, when Google began using GPS and related technologies to track the geo-location of every Android-based mobile device on earth (and every non-Android device, such as iPhones, that use the Google search engine, or a Google app like Maps) and store that information in a searchable database. The Sensorvault database thus contains precise historical location data for literally hundreds of millions of mobile devices worldwide, making it a treasure-trove for criminal investigators seeking to learn, for example, who may have been at or near a particular crime scene on or around a particular date or time. Moreover, the information stored in Sensorvault is readily available to law enforcement agencies via court-issued “geofence warrants” that are rapidly becoming routine tools in criminal investigation. According to Google, it received fewer than a thousand geofence warrants in 2018; by 2020, that number had ballooned to over 11,500.

Geofence warrants specify a defined geographic area – a particular house, for example, or even a city block – and a limited time period. Searching Sensorvault, Google then identifies any and all mobile devices present at the relevant time and place and codes them with anonymous ID numbers. If the requesting agency can show probable cause, the court will then order Google to reveal the users’ identities. Thus geofence warrants are sometimes called “reverse-location warrants” in that, unlike a typical search warrant, the process begins not with a particular suspect but rather works backward from a place and time to identify possible suspects. Moreover, once a particular mobile device has been identified, Sensorvault can continue tracking its movements outside the original geo-fence coordinates.

Geofence warrants are potential game-changers in criminal investigation, not unlike fingerprint and DNA evidence before them. And like those earlier innovations, the availability of geofence warrants and the Sensorvault database must be considered when plotting a credible crime story. For want of a less self-serving example, I’ll refer readers to my just-released legal thriller The Chimera Club, in which a geofence warrant and forensic genetics both are employed, and manipulated, along the serpentine path to catching a killer.

The upshot here is that we as crime writers must take a hard look at our works in progress. Is there a scene in which resort to a geofence warrant might help identify the killer? If so, are the police or FBI accessing Sensorvault? If not, then why not? We’re quickly reaching the point at which readers will be asking these very questions, and we as savvy storytellers had better have the answers baked into our novels or else risk the distinctive clunking sound of a tossed book hitting a reader’s wall.


Chuck Greaves, a former L.A. trial lawyer, is a Shamus, Lefty, Macavity, Audie, and Harper Lee Prize finalist and the author of seven novels including four installments in his Jack MacTaggart series of legal mysteries. You can visit him at

1 comment:

James Lawther said...

Fascinating article; I'm always a little disconcerted if and when Google asks me if I enjoyed my recent visit to a restaurant; I guess it is exactly the same principle.

What is the Sensorvault equivalent of wearing gloves? To switch your phone off? And if I level my phone at home, would that count as an alibi?

Not that I am planning anything, you understand.