Technology That Helped Catch Trump Suspect Is Proliferating

The suspect in the apparent assassination attempt on Donald J. Trump on Sunday was apprehended in part because of a technology that has been proliferating across the country: license plate recognition.

A witness saw the suspect drive away from the scene and gave the license number of his Nissan to the authorities, according to Sheriff Ric Bradshaw of Palm Beach County. Using that information, the sheriff said, license plate readers spotted the car heading north on Interstate 95 in neighboring Martin County. The police then blocked freeway exits and eventually stopped the driver, Ryan Routh, who has been charged with two federal gun crimes.

License plate readers — similar to technology used to collect road tolls in many areas — can transmit the location of a specific plate in real time, and store that data so that a vehicle’s location can be traced after the fact. They are now used by thousands of law enforcement agencies and capture billions of scans a year.

The police regularly trumpet the systems’ successes, such as finding stolen cars and responding to Amber Alerts for missing children. In San Francisco, which received a grant to install 400 license-plate cameras around the city, the police told The San Francisco Chronicle that they have used devices installed recently to make arrests in retail theft cases, a carjacking and a sexual assault.

Flock Safety, one of the country’s largest suppliers of the technology, says it works with more than 5,000 law enforcement agencies. Motorola Solutions, another large supplier, says it has more than 2,000 license plate recognition customers using more than 15,000 cameras that have performed more than 44 billion scans.

The technology to read license plates has been around since the