Since he attempted suicide before, I believe there is a big possibility that this is the cause of death. My heart goes out to his family and friends.
I read in the Express that they are going to treat this case as homicide due to the stuffed socks they found in the mouth of the victim, however I think it is plausible to think that maybe this young man did that so he could kill himself without noise and nobody comes to his rescue (since he already tried to unsuccessfully kill himself in the past).