If you cant be broadminded enough to answer from both sides then please don't comment 
1) if Jeremy was guilty and Julie was telling the truth - why would he tell her the story about the hit man? He previously had no problem with telling her he was going to kill his family by drugging them and burning the house down. He had told her on the phone that "tonight is the night" . She had lain in bed and in her own words she knew he had done it. So why would he tell her that a hit man was involved . In the eyes of the law the intent was the same So why would he do that?
2) If he is innocent who came up with the hit man story and why? Did it fit the crime in some way? And especially to come up with a name ?
1) I imagine Jeremy had told Julie that it was " probably " a hitman,because he himself couldn't fathom out what,or who had done this dreadful thing. Then between the two of them,they " possibly " rattled off a few names and came up with MM,simply because he'd done the dirty on Julies' friend,so it was a revenge thing. But,,did either of them consider what the REAL outcome of it would have been by blaming/naming MM ? I don't think so. It's something that wasn't thought through,so like it or not,his name was put forward ( did he ever sue,because I would have done ?)
How did Julie know that it was Jeremy ? Had he told her to keep certain things to herself ? Did she tell EVERYTHING there was to tell in court. Is,or has she been holding anything back all these years ?
Do we know the exact meaning of " tonight's the night ",from Jeremy himself ?
There were plenty of sleeping tablets at WHF which belonged to June,so why weren't just the mother and father murdered ? Why wait until the rest of the family were there ?
Why did Julie ask a deceased Sheila who'd done it ? Apparently both Julie and Sheila used to see a clairvoyant,so Julie was looking for an answer------------which I thought she already had !!