Well thought out, Tigger . I wonder too, if it could be proven that the person was so coerced as to be considered 'brainwashed' and manipulated to committing suicide OR murder, where the line (or lines) of responsibility fall.
Of course, there were cultists over the years, JimJones, CharlesManson, etc., where ppl did things seemingly under the influence of another person.
Then there are accounts of ppl being 'possessed' by demons, ... Think of at least one in the bible that was so badly under the influence he would easily break the bindings ppl would put on him, he would cut himself, (and think of the ppl who still do that today, many teenagers, sadly) and he would scream and hurl insults, etc., ..... Of course, ppl must have either hated or greatly feared this guy, yet Our Lord Jesus had compassion and ministered to him and set him free from that demonic influence.
I wonder how many ppl have gone beyond cutting themselves, to actually committing suicide, because of demonic coersion or possession.
But more to the point of the OP, suppose the person that coerced another to commit suicide was under demonic influence themself?
Gosh, I better quit now, it just gets muddier, and I don't know how much of these kind of things can be proven/disproved in a court of law.