I think any of these are possible:
(1) He killed himself by his own arrangement
(2) He was forced/cornered into killing himself and was provided with the assistance to do so
(3) He was murdered and had no hand in his own death

Regardless of which is true, there's corruption that needs to be investigated. At minimum, guards/the warden were paid off. I think it probably goes higher up than that. I don't have faith that the investigative processes will be free from corruption either. We will probably never know the truth of this.