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.
Cantor says it's unclear if the men were still inside the 27-story Metropolitan Correctional Center at the time.
Local shop owners say police swarmed the area around 8:30 a.m. Police said earlier in the day that Joseph Banks and Kenneth Conley appeared to have escaped between 5 a.m. and 8:45 a.m.
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.