2) All of that requires the consent of the person involved. Do you think AS would have suddenly decided to accept support because the DA prosecuting his case offered it? If his family and friends couldn't stop his suicide, you think the DA could have done so?
3) Are you sure it is typically the responsibility of the DA to sort that stuff out in the US?
See http://www.mind.org.uk/mental_health_a-z/8042_mental_health_... for an explanation of (in the UK, at least) the rights for those with mental health issues in prosecutorial circumstances.