An Oklahoma federal judge’s decision to throw out automatic license plate recognition (ALPR) evidence in a meth trafficking case last week is the most significant example to date of how a recent Supreme Court decision on geofencing will weigh on digital evidence and Fourth Amendment court proceedings moving forward, experts say.

Judge Sara Hill ruled October 1 that an arresting officer improperly used data from Flock brand ALPRs to build a case against Melisa Kyle — a decision heavily informed by the landmark June geofencing ruling, known as Chatrie, in which a majority of justices found that police searches of historical cell phone locations provided by third-party tech companies are limited by the Fourth Amendment.

Hill’s ruling that Flock searches are “approaching dragnet-type law enforcement practice” — and can be unconstitutional when conducted without a warrant — is a landmark finding on its own and, as with Chatrie, will influence judges considering future cases involving ALPR data, experts said.

The decision is one of the first times a federal judge has determined law enforcement searches for historic ALPR-collected data can violate the Fourth Amendment.

The Oklahoma decision does not set a binding precedent but is significant because it breaks from a consistent pattern of courts ruling that ALPR searches conducted without a warrant are acceptable under the Fourth Amendment since they don’t track everywhere a person goes minute by minute.  

Hill cited the June high court decision repeatedly in her opinion holding that officers need a warrant for some ALPR searches due to the fact that they capture citizens’ locations on a regular basis and are retroactively available to law enforcement.

In the Oklahoma case, a sheriff’s deputy stopped Kyle primarily because she had a California plate. He subsequently searched Flock to access an extended history of Kyle’s vehicle’s whereabouts, constituting what Hill called an “unconstitutional warrantless search” and an example of “indiscriminate mass surveillance.”

The arresting officer used Flock to quickly find 50 separate instances of Kyle’s car traveling in multiple states across a month-long period, according to Hill’s ruling. The Flock search was accessed without probable cause and violated Kyle’s constitutional rights, the opinion said, rendering the evidence found in a subsequent search of her vehicle inadmissible.