how many people escaped

3 escaped and have never been found again. They don't know if they are dead or not

I think they are few more than 3 but 3 tried more than once (if I heard correctly). But correct, nobody ever found any of them, i.e. they have never been found

Watch Escape from Alcatraz

They don't know it for sure because the bodies were never found, but aparently 3 guys