A rope dangles from a window on the back side of the Metropolitan Correctional Center on Tuesday in Chicago.

CHICAGO - The FBI says window prison bars were found inside a mattress in the cell belonging to two bank robbers who escaped from downtown Chicago's high-rise jail.

Tuesday morning's daring escape has prompted a massive manhunt for Joseph "Jose" Banks and Kenneth Conley.

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

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.

The affidavit says fake metal bars also were found in the cell, and that the cell's window was broken and had makeshift rope tied to its bars.