Julie did it- but not how you think.
Julie was obviously pretty sick of her life, her family, even friends and career probably. So, deciding to play along with the 'reckless' personality- she takes charge and turns it all around. I would love to say she lives now a normal and happy life, but here comes the fun part- JULIE. IS. BIGFOOT.
Not /actually/ bigfoot (well, actually, maybe... But that might be another theory), but she lives in the forest, causing chaos where needed. Burned evidence? Julie. Brendas poor poor truck? Julie. Probably more, probably disclosed or forgotten, small inconsistencies? Julie. Ralph?? Not Julie... But maybe something she was running away from?
And that Jeff... Geof? Goldbry? Jeff goldblum, the one who had the tire thrown at, helped julie! The inconsistencies in his stories are because he didn't want to betray her, and it would also explain the wig used as a disguise for her. The blood, however, could have been Ralph's (was it tested? Was Ralph's body tested?) Or even Julie's, maybe she was cutting out some kind of microchip from under her flesh (I knew celebrities must have had microchips!).
And Brenda: do you know or remember if any tips came through the years, "I saw Julie Capsom at this place and that place!"? Did any of them happen to be in a musty, dark, forest? A place where she, or any regular citizen, should not be? Her presence, maybe even, felt in the dead of night?