There is a lot of misinformation out there and there are many carve-outs that allow therapists to disclose this sort of information. For example, if someone is dangerous (as someone who has just impulsively murdered a girlfriend might be deemed), then they may disclose it. If there was a chance he would be a danger to himself (the danger of which is high in this situation), then they must disclose it. There is a lot of gray area and room for interpretation, but in practice, I don't know many therapists who would not find a compelling reason not to report in this situation, and I know, and have trained, lots of therapists.