If Gatti was going to kill himself then #1 Why hanging? #2 Why hanging by a purse strap and #3 Why on the stairs?

Sure he COULD have chosen all that being drunk and maybe drugged up, but it doesn't make sense to me. Too much work, it takes too long to die, and it could fail at any point in his trying it.

I think Gatti got to the apt, wanted to continue the argument with Amanda who by that time had called someone over to handle Arturo. Somebody confronts Gatti and perhaps (just perhaps) the guy knows ju jitsu (the Brazilians are big on it) and chokes Arturo out, but doesn't let go and you've got yourself an accidental homicide. Hell it could go any number of ways.