The Chicago police department operates an off-the-books interrogation compound, rendering Americans unable to be found by family or lawyers while locked inside what attorneys say is the domestic equivalent of a CIA black site.

The facility, a nondescript warehouse on Chicago's west side known as Homan Square, has long been the scene of secretive work by special police units. Interviews with local attorneys and one protester who spent the better part of a day shackled in Homan Square describe operations that deny access to basic constitutional rights....