Yesterday I posted speculation relating to the observation of one of the arresting officers in the Jun case (Roxane Gruenheid) that RE had an eastern accent. Based on public searches, it appears that Ms. Gruenheid may be from the Long Island, NY area - where many people have a distinct accent.
Theory of RE origin: He was raised in the tri-state area (outer burrough NYC, Long Island, NJ suburbs, Fairfield County CT), Providence area or Boston area. His accent was distinct enough to be recognizable in subtle ways to a native of the northeast area, but not pronounced enough to stand out to folks from CA as being remarkable. Hence his surprise at, having blended in so often in CA, to be called out by Ms. Gruenheid.
I further would guess that he originally hailed from a middle or upper-middle class family, somewhat belying his vagabond lifestyle and employment prospects as an adult. Very broadly speaking, strong regional accents suggest lower economic station; subtler accents suggest higher economic station, but likely rule out Manhattan or Philips Exeter. He was obviously intelligent, charismatic and well-spoken -- as most serial killers are -- social abilities that were possibly fostered in a comfortable enough upbringing, though they could of course simply be innate or learned in other settings.
Finally, I suspect extreme trauma or abuse in the early teen years for a prolonged period of time, events which caused a complete schism with family, the necessity of becoming self-sufficient as a teenager (electrical/mechanical skills, military enlistment) - courses that would in many cases have been avoidable for someone of his family's milieu.
I'm guessing he was from NYC environs (dead match to Ms. Gruenhein's ear) or Boston environs (familiarity with southern NH area allows him to "spread his wings" as a serial killer before desperation forces him to hit the road and adjust to itinerant circumstances in often unfamiliar turf).