My editorial: convicted thief who happens to have a knife on him is sent to jail. Decides to hang himself in his cell.

Obviously, this is the fault of everyone except the criminal and the family - more staff to look after these poor traumatised people!!! They are so shocked that they were finally caught they need councelling to make sure they are OK.
Point 1: This man was not convicted at all. He was "caught" shoplifting and admitted carrying a knife. Our legal system says he is innocent until proven guilty.

Point 2: He was showing clear signs of mental disturbance, and as Huruchai says, the state has a duty of care for those in prison, whether guilty or not. He did not receive that care and this contributed to his death.

They're in prison to be punished, not coddled and wrapped in cotton wool, and to be perfectly honest if they can't handle being in prison they should have thought of that before.
A yes, the "they should have thought of this before" argument. Trouble is that you can use it to justify any treatment once convicted: death penalty, torture, hard labour, limb amputation. All these, according to this argument, are fine because the person knew about them before. Also, how is it "punishment" to be allowed to commit suicide? As I said before, this man was not in prison for or even as punishment because he was on remand.