At the end, Johnny tells Lina that the reason he was inquiring about an untraceable poison was because he had it in mind to commit suicide. Maybe he's telling the truth, maybe he isn't. If he did intend to commit suicide by poison, is there a good reason why he'd want it to be untraceable?
"I beseech ye in the bowels of Christ, think that ye may be mistaken."
If he is in fact telling the truth about intending to commit suicide he probably would want the poison to be untraceable so that he would spare his wife the embarrassment and also for monetary reasons - insurance companies won't pay up if the death is ruled to be a suicide.
shareA good answer. One does wonder though if a genuinely suicidal Johnny wouldn't be more likely not to mess around with untraceable poisons but rather just drive (or jump) off the cliff, affording an interpretation of accidental death. To my mind the professed chosen means tends to increase doubts about the sincerity of the claim of suicidal intent.
"I beseech ye in the bowels of Christ, think that ye may be mistaken."