The idea in my head is that Charlie Sheen isn't Jamie, but instead of Vengeful Spirit created during Jamies murder that comes to the town to, much as a ghost or kitsune, clean up several issues in respects to Jamies death. It was created because both Billy & Keri bottle up their emotions/feelings about what happened and "summoned him". He heads to the quarry following his instincts of revenge and when he locks eyes with Packard he sees Packards "deepest secret" which is the murder of Jamie. He then uses his car to try and kill Packard but the lackey Oggie gets in the way and dies first. The Wraith "steals his soul" killing him personally before the crash finishes him off and then when watching the aftereffects one of his "braces" disappears, almost like a chain that is binding his spirit to the earth, and hopefully by killing all of the crew he can break all the chains and move on to the afterlife, kinda like the "unfinished business" in Casper. But, maybe just bad continuity/editing he shows up in a later scene and that brace that disappeared has reappeared, perhaps because Oggie didn't actually have something to do with the murder but the Wraith isn't sure since he just has the flashes to go off of. So instead he goes to the garage to try and gleam more information from the gang and threatens them with the shotgun, where he gets another flashback, different perhaps because it's from one of the other guys perspectives. So he takes some time to investigate more and eventually determines what he needs to do to break his chains: Kill Packard, Skank, and Gutterboy; save Keri from the awful relationship with Packard (and maybe a bit more); and say goodbye to his brother one last time before moving on.
