The didn’t ‘let him die’. They killed him. Even if they allowed him to off himself, they opened up a window of opportunity for him and told him to do ‘it’ then. Either he did it or someone else would do it for him.
Just like the Corleones...
Tom Hagen : When a plot against the Emperor failed... the plotters were always given a chance... to let their families keep their fortunes. Right?
Frank Pentangeli : Yeah, but only the rich guys, Tom. The little guys got knocked off and all their estates went to the Emperors. Unless they went home and killed themselves, then nothing happened. And the families... the families were taken care of.
Tom Hagen : That was a good break. A nice deal.
.………..my theory is the Mob did it and they did it for “the Clintons”and for “the Mob”. “HOW” they did it could have been something like “we’ve got your brother” and he’s toast unless you go under by tomorrow”. The Mob then ordered the jailer to discontinue the suicide watch.
Whatever! Few will EVER believe he did himself in or if he did it was with extreme coercion.