Grounds to Suppress ALPR Evidence

What a motion to suppress does

The exclusionary rule bars the government from using evidence obtained through an unconstitutional search or seizure. The Supreme Court applied it to state prosecutions in Mapp v. Ohio (1961): “all evidence obtained by searches and seizures in violation of the Constitution is, by that same authority, inadmissible in a state court.”

A motion to suppress is how a defendant asks the court to apply that rule. In federal court, Rule 12 of the Federal Rules of Criminal Procedure lists “suppression of evidence” among the motions that must be raised before trial when the basis is reasonably available. States have their own rules and deadlines. What happens at a suppression hearing walks through the process.

First question: whose rights?

Fourth Amendment rights are personal. Before reaching the merits, a court asks whether the person challenging the search had their own protected interest in what was searched. With ALPR data, which is about a vehicle, that can turn on who owned or lawfully controlled the car. In United States v. Yang, the Ninth Circuit held that the driver of an overdue rental couldn’t challenge an ALPR database search. See standing in borrowed and rental cars.

Ground 1: the stop

Many ALPR cases begin with a live alert. A traffic stop is a seizure, so officers need at least reasonable suspicion. The challenge usually focuses on what officers knew when they made the stop:

• Did the camera read the plate correctly, and did officers compare the image with the actual plate? Agency records show that a meaningful share of alerts are misreads. See plate misreads and accuracy.
• Was the hotlist entry accurate and still active? A car reported stolen and later recovered may stay on a list if the entry isn’t updated. See hotlists and alerts.
• Did officers confirm the hit before acting, as many agency policies require?

The legal standard and the cases that apply it are in traffic stops based on an ALPR alert.

Ground 2: searching stored data

The second kind of case begins after the fact, when investigators search stored reads to find a vehicle or trace where it went. The argument is that the search intruded on a reasonable expectation of privacy and needed a warrant. Carpenter v. United States required a warrant for historical cell-site records. The Massachusetts high court said in Commonwealth v. McCarthy that enough ALPR cameras could amount to a search, but held that four cameras didn’t.

The U.S. Supreme Court hasn’t decided whether ALPR use is a search, so this ground depends heavily on the facts and the jurisdiction: how many cameras, how much history, and what the query revealed. See is ALPR a Fourth Amendment search? and warrants and ALPR data.

Ground 3: a defective warrant

When police did get a warrant, for ALPR data or for a search that ALPR data helped justify, the warrant itself can be challenged. Two common grounds:

• False statements in the affidavit. Under Franks v. Delaware (1978), a defendant who makes “a substantial preliminary showing” that the affiant included a false statement “knowingly and intentionally, or with reckless disregard for the truth,” and that the statement was necessary to probable cause, is entitled to a hearing. In an ALPR case, that could mean an affidavit describing a camera read as a confirmed identification of a person.
• Lack of probable cause or particularity. The affidavit may not support probable cause, or the warrant may fail to describe what may be searched.

What else gets excluded

Suppression can reach beyond the first piece of evidence. Evidence found by exploiting the violation, such as drugs found after an unlawful stop or statements made during it, can be excluded as fruit of the poisonous tree.

It works the other way too. Finding a violation doesn’t guarantee suppression. Courts apply exceptions for good-faith reliance on a warrant, a database or precedent, for independent sources, for inevitable discovery, and for attenuated connections. See exceptions to the exclusionary rule.

Problems that aren’t suppression issues

A motion to suppress concerns how evidence was obtained. Many weaknesses in ALPR evidence are about what it proves: whether the read was accurate, whether the record is complete, and above all who was driving. Those questions are generally raised through discovery, cross-examination, expert testimony and argument at trial, not suppression. How the records can be admitted at all is a separate question under the rules of evidence.

Questions a defense attorney may investigate

• Did the case start with a live alert, or with a search of stored data?
• For an alert: what did the image show, what was the hotlist entry, and what did officers do to confirm it before the stop?
• For a search: how much data was queried, over what period, from which cameras, and under what authority?
• If there was a warrant: what does the affidavit say the ALPR data showed, and is that accurate?
• What evidence was found because of the stop or search?
• What is the deadline for pretrial motions in this court?

Whether to file a motion, and on which grounds, is a judgment for a licensed defense attorney who knows the facts and the local law. Questions to ask your attorney can help you prepare.