In Baltimore, Maryland, where law enforcement officials ought to be doing their utmost to win back the trust of brutalized residents who perceive a conspiracy against them, a shadowy police tactic is stoking more dark suspicions.

Thanks to Benjamin Shayne, an attentive Baltimore resident who noticed strange activity overhead, citizen sleuths have exposed "a previously secret, multi-day campaign of overhead surveillance by city and federal authorities during a period of historic political protest and unrest," the Washington Post reports. "Discovery of the flights—which involved at least two airplanes and the assistance of the FBI—has prompted the American Civil Liberties Union to demand answers about the legal authority for the operations and the reach of the technology used."

Some observers speculate that the planes used infrared technology to capture video images allowing police to track Baltimore residents at night, even in their homes. Others suggest that perhaps they used a device that allowed them to identify cell phones and track movements and the social networks of their owners. (I thought of the time a surveillance plane spied on all of Compton, California.)

The exact purpose of the Baltimore flights is unknown. The government will not reveal what it was doing. And that is unacceptable. Riots can justify unusual restrictions on liberty such as the temporary curfews imposed while order is restored. Had Baltimore police used a plane to help identify looters as they destroyed that CVS I wouldn't object. But a straightforward effort to videotape looters or impose a curfew or close off a particular street is transparent.