I'm not 100% but one fact that seems to support Minelli as a suspect is that Lisbon has remained unharmed to this day. Being as close as she is to Jane, it's a wonder she has not become an RJ victim by now. But Minelli and her were close and seemed to have a father-daughter bond so that may explain her relative safety. And that threat to Jane..to bring Lisbon's body with him? I don't think RJ every believed Jane would go through with that anyway so it was an empty threat on RJ's part.