Because he was on suicide watch, until conveniently taken off of it a few hours before he died.

His cell's camera also "mysteriously" stopped working.

Somehow, he hung himself, which should have been impossible at the facility he was in.

The odds make it extremely probably that he was "suicided", that is, murdered, and then have his death announced by a corrupt coroner as "suicide".

As it is, it seems like he was probably murdered by strangulation.