Automatic License Plate Readers and Flock Cameras in Massachusetts Criminal Cases

By Attorney Joe Serpa | Georgetown University Law Center | Massachusetts Criminal Defense Since 1995

Massachusetts police departments operate a growing network of automatic license plate readers, and prosecutors use the data these cameras collect as evidence in criminal cases. The cameras photograph passing vehicles, convert each plate to text, and store the plate number with the time, date, and location of the sighting. Officers query the stored records to place a specific car at a specific location on a specific day. That record can become central to the Commonwealth’s case.

Two matters drew attention in September 2026 to who controls this data. On September 14, 2026, the Boston Globe reported that outside law enforcement agencies were able to access Boston Police Department license plate reader data during a 2025 pilot program. The city’s contract with the vendor had required that access to be disabled. A bill pending in the Legislature would bar police from sharing the data with another agency except as required in a judicial proceeding. It would also bar them from obtaining another entity’s license plate reader data without a search warrant. A defendant facing charges built on license plate reader evidence can use these developments to test how the data in the case was collected and controlled.

How Automatic License Plate Readers Work

An automatic license plate reader is a camera paired with software that reads license plates. Some units are fixed to poles, bridges, and traffic signals. Others are mounted on police cruisers and read plates as the cruiser moves through traffic.

Each read creates a record. The record contains the plate number, a photograph of the vehicle, and the time, date, and location of the sighting. Vendors store these records in searchable databases. A single camera generates thousands of reads each day, and a regional network combines reads from many departments into one system.

Aggregation is what makes the stored data revealing. One read shows a car at one place. Thousands of reads across several weeks show a pattern of movement, including a driver’s home, workplace, and regular destinations.

Use of the Data in a Criminal Case

Prosecutors use license plate reader data to establish location and movement. In a case that turns on whether the defendant was present at a scene, a read that places the vehicle nearby at the relevant time supports the Commonwealth’s theory. In a case built on travel between two points, a series of reads can show a route.

Officers also use the data during investigations before charges issue. An officer queries a plate to learn where a vehicle has traveled, then builds the rest of the case from those leads. When the case reaches court, the reads may appear as exhibits, and the officer who ran the query may testify about what the database showed.

The evidence appears objective because it comes from a machine. That appearance of precision is a reason to examine the data closely. The reliability of a read and the lawfulness of the search that produced it are separate questions from the number on the screen.

The Constitutional Standard After Commonwealth v. McCarthy

The Supreme Judicial Court addressed license plate readers in Commonwealth v. McCarthy, 484 Mass. 493 (2020). The Court held that a person has a constitutionally protected expectation of privacy in the whole of their public movements under Article 14 of the Massachusetts Declaration of Rights. Widespread license plate reader surveillance can invade that interest.

On the facts before it, the Court found no search. The police used four fixed cameras at the ends of two bridges connecting Cape Cod to the mainland. Those cameras showed only whether the defendant was passing onto or off of the Cape at a given moment. The Court held that this limited surveillance did not permit the Commonwealth to monitor the whole of the defendant’s public movements, and it affirmed the denial of the motion to suppress.

The Court also described when the result would change. With enough cameras in enough locations, the historic location data from a license plate reader system would invade a reasonable expectation of privacy and would require a warrant, the same authority police must obtain to search a phone or computer. The Court explained that camera placement governs how invasive the surveillance becomes. Cameras near a home or a place of worship produce more revealing data than cameras on a highway. The Court declined to fix a bright line for how detailed the picture must be, which leaves the question open for litigation in each case.

The result is a fact-specific inquiry. The defense examines how many cameras contributed to the data, where those cameras stood, how long the records were kept, and how completely the combined reads mapped the defendant’s movements. The more complete the picture, the stronger the argument that the surveillance required a warrant.

Recent Massachusetts Developments

Two connected problems surfaced in 2026: unauthorized access to the data and misuse of the systems by officers.

On the access side, the Boston Globe reported on September 14, 2026 that outside law enforcement agencies were able to access Boston Police Department license plate reader data during a 2025 pilot program. The city’s contract had required that access to be disabled. Over the following five months the department received 77 requests for its data from other agencies. The department and the city have committed not to use the vendor going forward.

On the misuse side, reporting in 2026 has documented officers in Massachusetts departments, including Stow and New Bedford, using the databases to search for former partners. Reporting in 2025 described a Texas law enforcement agency searching the vendor’s nationwide network, including Massachusetts data, for a woman believed to have had an abortion. The sponsor of the pending House bill has cited out-of-state searches for people seeking reproductive or gender-affirming care as one reason for the bill.

On the local-control side, twenty-five Massachusetts municipalities have canceled contracts with the vendor Flock Safety or discontinued pilot programs over eighteen months, according to the American Civil Liberties Union of Massachusetts. The town of Boylston suspended its cameras in September 2026. A Suffolk County Superior Court judge has also ordered the Massachusetts State Police to release the audit logs of its license plate reader system and records of its camera locations.

These developments give the defense concrete facts to investigate. Where a department cannot show who accessed the data or under what authority, both the chain of custody and the lawfulness of the search come into question.

Proposed Legislation, House Bill 3755

Representatives Steve Owens and Lindsay Sabadosa filed House Bill 3755, An Act establishing driver privacy protections, in January 2025. The bill would regulate how law enforcement uses automatic license plate readers in Massachusetts.

The bill would prohibit anyone acting under color of state law from obtaining license plate reader data from another entity, governmental or private, without a valid search warrant. It would also prohibit disclosing the data or permitting access to it except as required in a judicial proceeding. It would bar the sale, lease, or purchase of the data. It would limit retention to fourteen days unless the records connect to a specific criminal investigation based on articulable facts linking the data to a crime. It would bar use of the technology to track or monitor activity protected by the First Amendment or by Articles II and XVI of the Massachusetts Declaration of Rights.

The House members of the Joint Committee on Transportation voted eleven to zero to report the bill favorably. The bill was referred to the House Committee on Ways and Means on March 23, 2026, where it remains. The provisions may be folded into a broader data privacy bill.

House Bill 3755 has not become law. The current rules for challenging license plate reader evidence come from Article 14 and McCarthy. The bill is relevant because its warrant and retention standards match the arguments the defense already makes under existing constitutional law.

Challenging License Plate Reader Evidence

The defense attacks license plate reader evidence on two fronts: the constitutionality of the search and the reliability of the data.

The constitutional challenge proceeds by motion to suppress. Counsel develops the extent of the surveillance, the number and placement of the contributing cameras, and the period the combined reads cover. Where the reads together show a detailed picture of the defendant’s movements, counsel argues under McCarthy that the collection was a search that required a warrant, and that the absence of a warrant requires suppression. Counsel also examines the lawfulness of any traffic stop that followed a read, and points to any outside agency that obtained the data without authority.

The reliability challenge tests the data itself. Automatic plate readers misread plates. Software can drop or transpose a character, so that the stored text shows a different plate than the vehicle photographed. Counsel compares the stored text against the photograph, examines the vendor’s error rate, and cross-examines the officer about the query and the database. Counsel also probes the chain of custody, because a record accessed and shared outside proper channels may be unreliable or inadmissible.

Where the motion to suppress succeeds, the location evidence leaves the case. Where the reliability challenge succeeds, the fact finder gives the evidence less weight at trial.

Obtaining the Records in Discovery

A person charged with an offense that rests on vehicle location should assume that license plate reader data may be part of the file. Counsel obtains the underlying records in discovery, including the reads, the photographs, the query logs, and the records of who accessed the data. Those materials determine whether a motion to suppress is available and whether the data can be challenged for accuracy. The same suppression practice governs a warrantless search of a vehicle and a motion to suppress in a motor vehicle stop.

Attorney Joe Serpa reviews the discovery in each case for evidence of this kind and litigates the constitutional and reliability questions the records present.

Key Takeaways

• Massachusetts police use automatic license plate readers, and prosecutors use the reads as evidence of a vehicle’s location and movement.
• In Commonwealth v. McCarthy, 484 Mass. 493 (2020), the Supreme Judicial Court held that a person has an Article 14 privacy interest in the whole of their public movements, and that a dense enough camera network can be a search requiring a warrant.
• The defense challenges this evidence by motion to suppress and by testing the accuracy of the reads.
• Reports in 2026 of unauthorized access to Massachusetts license plate reader data give a defendant new facts to investigate in a suppression motion.
• House Bill 3755 would require a search warrant before police obtain license plate reader data from another entity and would limit retention to fourteen days. It would also bar disclosure of the data except as required in a judicial proceeding. It has not become law.

Related Serpa Law Office Resources

• Illegal Searches and Seizures in Massachusetts: Article 14 and the Motion to Suppress
• Phone, Computer, and Digital Searches in Massachusetts
• Massachusetts Traffic Stops, Exit Orders, and Pretext Searches
• The Modern Massachusetts Traffic Stop: Phones, GPS, License Plate Readers, and the Fruit of the Poisonous Tree
• A Practitioner’s Guide to the Motion to Suppress in Massachusetts Motor Vehicle Stops
• Can Police Search My Car in Massachusetts Without a Warrant?
• Digital Search Warrants in Massachusetts