From what I can tell, LE is NOT treating Jason as a suspect but there is certainly a cloud of suspicion hanging over him. True, young men have been known to kill their girlfriends out of jelousy or whatever but how many hire a "hit team" to do it? The police could have checked Jason's finacial records (that is SOP when a hired "hit" is suspected). Hiring an attorney is not as suspicious as it sounds; it is actually a very prudent thing to do if you fear you might be a suspect. Jason did cooperate with the police, he even let them film a re-enactment.
The possibility that Jason's mother is involved is way off the chart. Why would a mother participate in the murder of her son's girlfriend? (apparently there was no money involved, no children: I am assuming Lindsay wasn't pregnant, no property, Life Ins etc) There just isn't a plasible motive.
The Calgary Drug Dealer is interesting. We know of no reason to believe that he may have suspected her of "ratting him out" or if she was otherwise involved in drug dealing. It would not be that unusual for a young Professional woman to use cocaine or "socialize" with guys who deal the stuff; if would be unusual for someone like her to be in so deep that they would be murdered. I would assume this angle has been checked out.
My WAG (wild *advertiser censored* guess) is that this was a sexually related murder by a stranger who saw Lindsay's picture on a Real Estate Advert and set her up to meet at a vacant house that the perp(s) would have had no known ties to. This could be a very hard case to solve.