One could make the argument that as a District Attorney he would know that it is possible to ruin a person's life without ever stepping in a courtroom. He would know that a false accusation, once broadcast on national TV, is as good as fact, and that the accused life is irretrievably ruined.
Who knows? Perhaps there was even a fair measure of self-loathing involved because he had managed to stupidly get himself involved in this horrendous situation.
We will never know. The man is dead.
I'm not convinced of his guilt or innocence. But you are making this guy out to be completely incompetent. I give him more credit than that. Being innocent and with his experience as a District Attorney, he would know what would need to be done in order to clear his name. Evidence abounds in a case like this. Just by looking at the transcript(s) of his chat(s) with someone he thought was a 13 year old boy will help reveal what he was up to before he committed suicide.
On the surface I think NBC was foolish to go to the man's home as were the police (unless they had damning evidence requiring immediate action).