I agree with all dungbeetle has said here. The extent of the self harm indicates a need for a mental health assessment. Also, being a mental health professional in a forensic setting myself, I would raise the possibility of false confession which is more common than may be imagined. The patient gave no specific details, only a vague and 'dramatic' statement. If I had been there I would have handed over the full story to those doing the psychiatric assessment. You had no evidence to suggest he had done anything other than harm himself. Had he been quite specific I may have reported it to the police but I would inform him (Pt) that I intended to do so.