In eight years as a federal magistrate judge in Texas, Brian Owsley approved scores of government requests for electronic surveillance in connection with criminal investigations—then sealed them at the government's request. The secrecy nagged at him.

So before he left the bench last year, the judge decided to unseal more than 100 of his own orders, along with the government's legal justification for the surveillance. The investigations, he says, involved ordinary crimes such as bank robbery and drug trafficking, not "state...