ALPR Data and the Fourth Amendment: What United States v. Mapson Actually Decided
ALPR data Fourth Amendment questions have become genuinely urgent as automatic license plate readers spread across the country, and a recent federal appellate decision illustrates exactly how unsettled this area of law remains. The case is United States v. Mapson, 96 F.4th 1330 (11th Cir. 2024), and it involves one of the more unusual fact patterns to reach a federal court of appeals in recent memory.
Three sisters, Tierzah, Charis, and Elisa Mapson, faced federal charges connected to a shooting scheme targeting Joshua Thornton, the father of Tierzah’s daughter. Thornton and Tierzah had arranged to meet at a small gas station in Alabama, roughly halfway between their respective locations, to exchange custody of their child. While Thornton waited, someone shot him. He survived, but the shooting launched a federal investigation that eventually implicated all three sisters in what prosecutors described as a coordinated plot connected to their ongoing custody dispute.
Facing Charges Where the Government Used License Plate Data Against You?
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How ALPR Data Became the Key Evidence
When investigators looked into the shooting, one of the sisters initially told police she had been in Florida the entire time, nowhere near Alabama. That story ran into a serious problem once investigators pulled data from automatic license plate readers, commonly called ALPRs. These systems, some operated directly by law enforcement and others run by private companies that contract with police departments, photograph passing vehicles and their license plates on public roads, then store that data for later reference.
The ALPR records told a very different story than the sister’s initial statement. Her license plate showed up traveling along a specific interstate route, through Georgia, and directly toward the small Alabama town where the shooting occurred. That data became central to connecting her to the crime scene despite her claim that she’d never been anywhere near it.
The Fourth Amendment Argument on Appeal
After the sisters were convicted, they appealed, arguing that the government never obtained a warrant before acquiring this ALPR data, and that its use violated their Fourth Amendment right to be free from unreasonable searches and seizures. This argument drew heavily on Carpenter v. United States, 585 U.S. 296 (2018), where the U.S. Supreme Court held that the government’s acquisition of historical cell-site location information constitutes a search requiring a warrant, precisely because that kind of data reveals an intimate, detailed picture of a person’s movements over time.
The sisters argued that ALPR data functions similarly, building up a comprehensive record of someone’s movements across public roads over an extended period. If cell-site data requires a warrant because it’s so revealing, they argued, license plate data compiled across multiple states and multiple points in time should require the same protection.
What the Eleventh Circuit Actually Decided
Here’s where the ruling gets genuinely interesting, and where it’s important to understand exactly what the court did and didn’t decide. The Eleventh Circuit didn’t definitively rule on whether acquiring ALPR data constitutes a Fourth Amendment search requiring a warrant. Instead, the court assumed, without actually deciding, that the warrantless acquisition of this ALPR data might have violated the Fourth Amendment under the Carpenter framework. Having made that assumption, the court then resolved the case on a separate, narrower ground: the good-faith exception to the exclusionary rule.
Under the good-faith exception, evidence obtained through a search that might otherwise violate the Fourth Amendment can still be admitted if law enforcement relied in good faith on the state of the law at the time, particularly when courts hadn’t yet clearly established that a warrant was required for that specific kind of data. Because so little existing case law addressed whether ALPR data acquisition required a warrant at the time investigators pulled this information, the court found that officers acted reasonably and in good faith, regardless of how the underlying constitutional question might eventually get resolved. The court noted directly in its opinion that very little case law or academic literature existed addressing whether ALPR data acquisition constitutes a Fourth Amendment search, and used that genuine legal uncertainty to support applying the good-faith exception.
Why the Underlying Question Remains Open
This means the core constitutional question, whether the government needs a warrant to acquire ALPR data documenting someone’s movements across state lines, remains formally unresolved after Mapson. The court sidestepped deciding it by resolving the case entirely on good-faith exception grounds instead. The convictions stood, but the door remains open for a future case, likely one where the good-faith exception doesn’t apply, to force a definitive ruling on whether ALPR data acquisition itself requires a warrant.
This is a meaningfully different outcome than a court simply declaring ALPR data isn’t private enough to warrant Fourth Amendment protection. Rather, the court left that specific determination for another day while resolving Mapson’s case on a technical, procedural basis instead.
What This Means Going Forward
Anyone facing charges where ALPR data played a central role in the investigation should understand that this area of law remains genuinely unsettled. The government’s argument that ALPR data simply documents vehicles traveling on public roads, information theoretically visible to anyone, competes directly against the argument that aggregating this data across time and location creates exactly the kind of comprehensive movement profile the Supreme Court found so troubling in Carpenter. Until a court directly resolves this question outside the shelter of the good-faith exception, defense attorneys handling cases involving ALPR evidence should continue raising this Fourth Amendment challenge, since the underlying question remains a live one.
If You Want More Related Content
Check out our more videos and breakdown articles covering major updates in Florida defense law. You can also use the links below to stay informed. Learn how to protect your constitutional rights when dealing with law enforcement.
Watch: Understanding Probable Cause and Search Warrants in Criminal Cases
Read: https://jgcrimlaw.com/articles/secret-federal-warrant-florida-cabrera-fourth-amendment/
John’s Takeaways
- United States v. Mapson, 96 F.4th 1330 (11th Cir. 2024), did not resolve whether ALPR data acquisition requires a warrant under the Fourth Amendment. The court assumed a violation might have occurred but decided the case on other grounds.
- The court applied the good-faith exception to the exclusionary rule, finding officers acted reasonably given how little existing case law addressed this exact question at the time.
- Carpenter v. United States, 585 U.S. 296 (2018), established that historical cell-site location data requires a warrant because it reveals a detailed picture of someone’s movements over time. The sisters argued ALPR data functions similarly.
- The core constitutional question about ALPR data remains formally open. A future case without the shelter of the good-faith exception will likely be needed to force a definitive ruling.
- Defense attorneys handling cases involving ALPR evidence should continue raising Fourth Amendment challenges, since this area of law hasn’t been settled and the underlying question remains genuinely live.
Facing Charges Involving License Plate Reader Evidence in Central Florida?
I’ve been following Fourth Amendment developments involving new surveillance technology across Central Florida since 1993, and this remains one of the most genuinely unresolved areas of search and seizure law today. I represent clients across Orange, Seminole, Osceola, Lake, Brevard, and Volusia County.
Give my office a call. Let’s talk through how ALPR evidence factored into your case and what challenges might still be available.
John Guidry — (407) 423-1117
About John Guidry II
John Guidry II is a seasoned criminal defense attorney and founder of the Law Firm of John P. Guidry II, P.A., located in downtown Orlando next to the Orange County Courthouse, where he has practiced for over 30 years. With more than three decades of experience defending clients throughout Central Florida since 1993, Guidry has successfully defended thousands of cases in Orange, Seminole, Osceola, Brevard, Lake, and Volusia counties. He has built a reputation for his strategic approach to criminal defense, focusing on pretrial motions and case dismissals rather than jury trials.
John Guidry earned both his Juris Doctorate and Master of Business Administration from St. Louis University in 1993. He is a member of the Florida Bar and the Florida Association of Criminal Defense Lawyers. His practice encompasses the full spectrum of Florida state criminal charges, with a particular emphasis on achieving favorable outcomes through thorough pretrial preparation and motion practice.
Beyond the courtroom, Guidry is a prolific legal educator who has authored over 400 articles on criminal defense topics. He shares his legal expertise through his popular YouTube channel, Instagram, and TikTok accounts, where he has built a substantial following of people eager to learn about the law. His educational content breaks down complex legal concepts into accessible information for the general public.
When not practicing law, Guidry enjoys tennis and pickleball, and loves to travel. Drawing from his background as a former recording studio owner and music video producer in the Orlando area, he brings a creative perspective to his legal practice and continues to apply his passion for video production to his educational content.