12:09 PM PT -- A prison source tells us Bulger -- who is wheelchair bound -- was in general population Tuesday morning. We're told he was approached by 3 other inmates who wheeled him into a corner that could not be seen by surveillance cameras.
Our source says the inmates beat Bulger -- one used a lock in a sock as a weapon -- until he was unconscious. They also attempted to gouge his eyes out with some type of shiv, but were unsuccessful. Bulger fell to the ground covered in bruises and with several dents in his head.