The problem is that even then you'll be able to get people to dismiss it with a "well, but he was mentally disturbed enough to lie about what we did, so clearly

The problem is that even then you'll be able to get people to dismiss it with a "well, but he was mentally disturbed enough to lie about what we did, so clearly he just wanted to get one last dig in when he committed suicide". In other words, I don't think it'd be any significant deterrent to anyone prepared to call in a hit - anyone ready to do that would already have accepted that it will look dodgy and be prepared to counter it by smearing you. If you want to deter a hit in a situation like that, I think the only way to do that is to ensure you have very significant additional data (or at least convincingly imply you do) and make it clear they'll be released if you "commit suicide".