Thought Mugford told him to not be stupid & go back to bed.
The relatives think the same as me. They believe that Mugford thought Jeremy was not serious.
No, she said that when he called later in the night - allegedly after the murders.
So the relatives (and you) think that even after the murders, Julie did not think Jeremy was serious? He had been talking about this for a year, calling her to tell her that he was going to do it tonight, even calling her after the fact to say it was done.
You really have to excuse her every step of the way. What about the sleeping pills she left at Jeremy´s home after he had talked about, well, giving his family.... sleeping pills, then burn the house down. How much can you excuse Muggie? Unbelievable, really!