A number of theories as to the EAR/ONS background have been put forth over the years. Below are a few of the more prominent ideas along with the general reasoning behind them.
The suspect was proficient with firearms. His MO suggests the possibility of military training. At least one victim described him as possessing a “military bearing". There are military installations near areas of attacks. Several of the EAR victims in the Sacramento area had some military connection.
The neighborhoods of virtually every attack had homes for sale or under construction. There were paint smudges found at three rape scenes in the Sacramento area and three of the murders in the Irvine area. Some of this paint was determined to be architectural paint, probably from an industrial paint sprayer. It's possible the killer worked various construction jobs, possibly as a painter, around the state, explaining how and why he remained in one area for months before moving on to another.
Almost every neighborhood the EAR targeted had homes for sale, sometimes the target home itself. Suspicious young men were reported on a few occasions in areas of EAR attacks claiming to be realtors or prospective buyers.
Around half of the victims were either employed in the medical field or had had some recent contact with it, this includes visits to hospitals, pharmacies, etc. EAR knew the alternate name for a victim’s prescription pain medication, suggesting some pharmaceutical knowledge.