The FBI and the Defense Department were actively involved in research and development of facial recognition software that they hoped could be used to identify people from video footage captured by street cameras and flying drones, according to thousands of pages of internal documents that provide new details about the government's ambitions to build out a powerful tool for advanced surveillance. The documents, revealed in response to an ongoing Freedom of Information Act lawsuit the American Civil Liberties Union filed against the FBI, show how closely FBI and Defense officials worked with academic researchers to refine artificial-intelligence techniques that could help in the identification or tracking of Americans without their awareness or consent. Many of the records relate to the Janus program, a project funded by the Intelligence Advanced Research Projects Agency, or IARPA. The improved facial recognition system was ultimately folded into a search tool, called Horus, and made available to the Pentagon's Combating Terrorism Technical Support Office, which helps provide military technologies to civilian police forces. No federal laws regulate how facial recognition systems can be used. The tool's use in domestic mass surveillance would be a "nightmare scenario," said Nathan Wessler, a deputy director at the ACLU. "It could give the government the ability to pervasively track as many people as they want for as long as they want. There's no good outcome for that in a democratic society."