You've made some very good posts Maggie.
Jeremy was easily led and his previous " petty crimes " were carried out for the excitement and fun that he got out of it,,similar to the naughty schoolboy who carries out things for a dare,,,he just wasn't/isn't the type to resort to murder,,as I find it impossible to envisage him killing one person,let alone five.
His mouth ran away with him just because he thought out loud and JM used this downfall against him. He may have said all kinds of things in the past,but not in the context in which it ended up in court.
With friends like JM,you don't need enemies.
Maybe Brett Collins often thinks about Jeremy,I don't know,,but JM had spread the word that Jeremy was bi-sexual because of his looks and charm,and that she'd said that Jeremy told her himself. Nevertheless, she wasn't fussy at the time though. Strange,that.