Yes, it seems unlikely LE would release this kind of evidence from their cold case files, especially when they have little or no other evidence from the crime scene(s). I wonder if LE retrieved anything helpful from Dorothy's car?
The theory about the person (Mike Butler?) who was a cult member seems somewhat plausible, but would he have access to a car? Whomever stalked, kidnapped and killed Dorothy needed a car. They also had to do a lot of walking that night, from alley where they left her car back to where they parked in the hospital parking lot or somewhere nearby. Also, if they dumped her body along the freeway with the remains of a dead dog, how did that work? Did they bring along their own dead dog when they went to kidnap her? Did they just happen to come across a dog they could kill while in the process of kidnapping and killing her? Just an odd thing to try to fit in during a very busy night for the killer. Did he just dump her body that night, then come back later with the dead dog to bury with her? Next to a busy highway?
The theory about it being the GSK is interesting, though it doesn't fit his MO - attacking victims in their homes and leaving bodies there. The other personality characteristics of the killer seem very similar, especially exerting power and control over victims before and after the murder.
GSK/DeAngelo has made us understand more about LE who commit murders. What if this wasn't GSK, but was another rogue LEO? "Head shops", etc. were probably prime targets for LE to keep under surveillance in those days, looking for drug dealers and users. What if the killer was an undercover investigator for a law enforcement agency whose job was to spend a few months staking out the two shops where Dorothy worked? What if he became "obsessed" with her instead, deciding to stalk and eventually kill her.
It would fit with some of the characteristics of GSK, but with unique MO more compatible with someone working undercover. Same skill set, knowledge of how to make phone calls that can't be traced, disguising his voice, blending into the neighborhood, being close by but not standing out. Skills at listening to other people's conversations, maybe even had a "bug" planted in the stores, so would have heard employees discussing plans, meetings, etc. Ability to follow a victim, hide and abduct them without causing a big scene or attracting attention.
As part of his job surveilling the stores, he may have even posed as a customer on numerous occasions, making his voice familiar to Dorothy. The taunting of the victim would suggest he had become familiar with her, felt her inferior to him as she worked in a "head shop", etc. JMO, lots of hints for an LEO in this.
Wonder if there were any similar crimes, sexual assaults, etc. in the area? Any odd members of LE (local, county, state or federal) working undercover in drug stings back then?