The American Civil Liberties Union has obtained documents from the Federal Bureau of Investigations that detail the surveillance flights made by FBI-operated aircraft over Baltimore last May. The flights included both high-resolution optical and infrared surveillance and at least two electronic surveillance flights, though the exact nature of the sensors used on the electronic surveillance flights was redacted from the documents.

The collection of records, which includes flight logs, evidence logs, and an FBI memorandum justifying the flights, was obtained by the ACLU through a Freedom of Information Act filing on May 6. The aircraft, which were registered to FBI front companies that are used to conceal the identity of the aircraft flown by the FBI's Special Flight Operations branch, flew day and night missions over the areas where protests were taking place in Baltimore—areas where riots broke out the previous week after the death of Freddy Grey in police custody.

The records show that the FBI not only provided live video intelligence to the Baltimore police, but also collected and saved high-resolution video footage of hundreds of people participating in protests on the streets of Baltimore—footage that may be used in the future to build profiles on those people. The records offer a look inside the FBI's secret surveillance operations that span the country, carrying not just cameras but electronic sensors such as "dirt boxes" that can track cell phones on the ground and potentially intercept calls.

In the electronic memorandum filed by the FBI, accompanying evidence records from the surveillance, FBI officials described their reasoning for the aerial surveillance:

Social Media streaming and intelligence has indicated that large scale demonstrations and protests are being scheduled for Baltimore and the surrounding areas. The potential for large scale violence and riots throughout the week presents a significant challenge for the Baltimore Police Department for airborne surveillance and observation. Baltimore will request the assistance of [the FBI's Critical Incident Response Group] and [Washington Field Office] in the matter of airborne surveillance to assist the Baltimore Police Department. Baltimore has continued to evaluate threat streams, intelligence, canvass sources and follow all actionable leads.

The memo also described social media posts calling for a "purge" at the Security Square Mall west of Baltimore—near the FBI's Baltimore Field Office. The memo noted that "several known 'Sovereign Citizens' have begun to post and send social media information attempting to rally persons to demonstrate in front of the Baltimore Field Office on Friday, May 1, from 1:00pm-6:00pm." The so-called "purge" never took place. However, the flights may have played a role in the enforcement of the curfew imposed on Baltimore by Governor Larry Hogan and in the monitoring of other protests within the city.

Flying panopticon

The ACLU filed the FOIA requests, both with the FBI and the Federal Aviation Administration, out of concern that the FBI was using surveillance gear that would allow agents to look into buildings and homes from above. While the FBI has claimed that aerial surveillance is allowed without a warrant under the Fourth Amendment because they are recording things that are in plain sight, the gear used by the FBI's surveillance aircraft included infrared cameras and other gear that could have detected activity within structures. And electronic surveillance may have been used to gather data on individuals taking part in the protests that were surveilled.

"Use of infrared and night-vision camera technology changes the equation by raising the potential for invasions of privacy," ACLU Staff Attorney Nathan Freed Wessler wrote in a blog post going up today. "The capabilities of the surveillance gear matter. If the infrared camera is capable of observing information about the inside of private homes and offices, for example, the Supreme Court has already explained that the Fourth Amendment’s warrant requirement applies."

As Ars reported in May, the FBI's surveillance aircraft carry a number of optical sensors, including a suite of daylight and infrared electro-optical cameras from L3 Wescam and FLIR. One of the aircraft identified in the documents in the FOIA response—a Cessna 182T registered to the company NG Research—carried a FLIR Talon multi-sensor gimbal, capable of capturing high-resolution images day or night, and automatic target tracking, according to FAA documents on alterations made to the aircraft.

The FBI records show 10 surveillance flights over Baltimore between April 29 and May 3. In total, the FBI logged 36.2 flight hours over Baltimore. In addition to providing live information about activities on the street, the aircraft recorded hours of video, forwarding copies to the Baltimore FBI field office's electronic surveillance unit. (Ironically, some of the video was sent to the Washington Field Office, which oversaw the flights to Baltimore. The Baltimore unit didn't get copies of the video until May 11.)

However, evidence records for flights on April 29 and May 3 list the material collected as an SD card containing what was described only as "other electronic surveillance." While this is likely just infrared surveillance footage, the flights may have gathered other data as well from electronic sensors.

Wessler noted that some of the concerns over the FBI flights included "what data were they gathering and saving, with whom is that information shared, and whether aerial surveillance has the effect of chilling First Amendment–protected speech and assembly." He added that the flights also raised "concerns about whether the intelligence gathered could lead to racial profiling of protesters, who are predominantly people of color."