CHICAGO (AP) - Two inmates who escaped downtown Chicago's high-rise federal jail by climbing down a rope may have fled hours before police swarmed the area.

U.S. Marshal's Service spokeswoman Belkis Cantor says the convicted bank robbers were first unaccounted for during a 5 a.m. head count Tuesday.

Tuesday morning's daring escape has prompted a massive manhunt for Joseph "Jose" Banks and Kenneth Conley. An FBI affidavit filed late Tuesday says the men shared a cell, and that their beds contained clothing and sheets stuffed under a blanket that appeared to look like a body.

Cantor says it's unclear if the men were still inside the 27-story Metropolitan Correctional Center at the time.

The two men apparently squeezed through a narrow window and scaled down about 20 stories using a rope possibly made of knotted bed sheets.

Hours later, a rope, possibly fashioned from sheets and then knotted at six-foot intervals, could be seen dangling from a window about 20 stories up.

The FBI says window prison bars were found inside a mattress in the cell belonging to two bank robbers who escaped.