As far as I know lie detectors are used within the legal system I am sure probation officers have used them
As far as Julie mugford and a jury believing her I had the unfortunate of being part of a jury on a murder case at Chelmsford crown court and a frightening fact I observed was a number of the jurors made it quite clear they thought he looked guilty and a few really didn't understand the case, when you are tried by jury it is pot luck Jeremy was convicted on 10-2 majority from what I have read I have no doubt that the jury would have felt different if more information had been disclosed. I will never understand the way Julie mugford was treated look at the way Maxine Carr was treated she got a prison sentence and she wasn't involved as much as Julie mugford and there were two girls involved there, not 5 murdered. I am quite sure she didn't sell her story either. I believe the police had a very flimsy case against Jeremy and were quite happy to let jm off anything as long as they got a conviction on Jeremy and it looked like well done Essex police.