I think we are confusing 'responsible for his death' with 'the cause of his death'

The mental anguish of being ruthlessly sued by a government, with the cooperation and possible collusion of your school, and facing the potential for many years in prison is inarguably substantial. How well would you have handled the same thing?

Whether a more stable person would have been able to suck it up is inconsequential - they still did the damage that they did. In his case, it was too much. The damage is there either way. They may not be responsible for the ultimate outcome, but they are responsible for the anguish that put him there.