The kind of person who wants to cause mass harm is the kind of person who's thought about it for more than 15 minutes. If you think about it for more than 15 minutes, I'm sure you can come up with plenty of ways. (Even 5 minutes is probably long enough to produce 3 or 4 workable suggestions.)

If AI causes people to kill who otherwise wouldn't have, I expect it to be by causing and exacerbating mental health problems, not by providing knowledge. (See e.g. https://www.bbc.co.uk/news/technology-67012224, where a roleplay escalated into a concrete plan to kill Queen Elizabeth II over the course of two weeks. The plan wasn't, however, a very good one.)