Comparing rates of attempted and completed suicide between the prison and general population is tricky, partly because access to means and methods should be much harder in prison.

But why are the rates of attempted or completed suicide so high?

I think mpyne was saying that there are plenty of people that go through the legal system and don't kill themselves. I don't think it had anything to do with comparing suicide rates in prison with other people. But instead pointing out that many, many, many people who are facing prison do not kill themselves. Some do. (adding my own opinion) But some people also kill themselves when facing divorce. Or job loss. Or Christmas. Depression is an illness. Depression lies.