A scan of 10 million Maryland ID photos turned up his identity.

Some background: After a man killed five members of the paper’s staff last week, authorities quickly apprehended a suspect. He did not have an ID on him, refused to cooperate with police, and couldn’t easily be recognized via his fingerprints, so they turned to face recognition software.

How it worked: Police sent a photo they took of the suspect to the Maryland Coordination and Analysis Center, which compared the image with 10 million driver’s license and ID photos in the state’s database. The system came back with a match: Jarrod Ramos. “We would have been much longer in identifying him and being able to push forward,” said Timothy Altomare, chief of the Anne Arundel County Police Department, on why the technology was used.

Why it matters: It’s proof positive that face recognition tech can be useful for law enforcement agencies—but it also raises many privacy questions over how widely they should be able to use the tool. The FBI, for example, currently has access to 16 states’ ID photos.