While protesters were flooding the streets last spring, the FBI flew 10 secret surveillance flights over the city.

The ACLU obtained information about and footage of those flights thanks to a Freedom of Information Act request. The FBI registered the planes using shell companies, and generally flew high enough that they wouldn’t have been noticed by on-the-ground observers. While the footage occasionally tracked individual cars and people, magnification doesn’t enable you to see individual faces.

“At times, the cameras followed individual people walking or cars driving through the city,” the ACLU reports. “There are undoubtedly situations where aerial surveillance by law enforcement is appropriate, but there should be protections against mass surveillance of people engaged in First Amendment-protected protests and gatherings.”

“The aircraft were specifically used to assist in providing high-altitude observation of potential criminal activity to enable rapid response by police officers on the ground,” FBI spokeswoman Amy Thoreson said, according to the Baltimore Sun. “The FBI aircraft were not there to monitor lawfully protected First Amendment activity.”

The ACLU’s report is just the latest revelation about increasing aerial surveillance. The FBI flew similar flights over other protests last year.

If you want to watch the footage yourself, it’s available here — all 18 hours of it.