Do you think Jeremy is guilty but never spoke about it to Julie?
If Jeremy is gulity Julie was on board and only went to police not out of sadness for Nevill June the boys and Shelia but out of jealousy that Jeremy was going with other women and didn't want to carry on with her. She may have also felt the net would close on Jeremy sooner or later and may have wanted to prematurely present a picture better than what could have eventually been painted.
Giving EP a sanistised version of events in regards to her own feelings minimising her own true feelings and involvment.
Knowing Jeremy would have never confessed as I have retierated.