The Next Morning
The Alcatraz authorities were dumbstruck when they discovered that the prisoners were gone the next morning. They interrogated and tortured every prisoner that had any sort of relationship with the convicts until they got some information about their escape. The cops couldn't figure out how the trio actually managed to get off of the roof, but they got a tortured inmate to say that the trio had constructed a raft out of raincoats and they were headed towards the closest island to the penitentiary.
Surveying the Area
All that was reportedly found by the police that day was a singular home-made life vest, a makeshift paddle, and bits of plastic that were assumed to be part of the raincoat-raft. The cops called their search a victory, they assumed that nobody would have been able to survive a swim across the San Francisco Bay. They stated, with the utmost confidence, that the prisoners had died while trying to escape on the raft...