While there is no doubt in my mind that Donny had something to do with the murder of his sisters, I am on the fence as to whether he did it himself or had someone else do it. Donny's mother heard him telling someone to get out of there and the neighbor saw two unidentified men fleeing the scene. I definitely do not buy that they just showed up randomly, found Donny's gun and gas can and capriciously decided to set the house on fire and kill the girls. It does seem odd that they wouldn't have brought their own stuff. If they had, it's very doubtful anyone would have suspected Donny being involved but he doesn't strike me as being very bright. Does anyone know if Donny had any kind of criminal record prior to the incident? If he did, it wasn't mentioned on the show but as we all know, Unsolved Mysteries was notorious for leaving out details on cases. I also have a feeling that if Julie hadn't died before she could be cross examined, Donny would most likely have been convicted. Without her testimony, the prosecution had a tough case. If Donny was convicted and there were others involved, I'm sure he would have snitched on them

I still think it's a plausible theory how (if Donny was not involved) the perpetrators were passing by the Hansen house and saw a crime of opportunity. Remember the Texas killing spree teenagers case? They used weapons and vehicles taken from each of the victims to carry out their dirty deeds.