Interesting points, all. For arguments sake I'll start with a generic definition of an Organized Serial Killer. I believe that this particular individual loosely fits the definition.
This offender will perpetrate very deliberative crimes, thoroughly calculated and planned. Premeditation of these crimes will also typically include extensive stalking. He preys mostly on strangers so that he cannot be linked to their victims in any way. He will hunt far from work or home, but in an area he has surveilled and become intimately familiar with. The abduction and abuse of the victim will be perpetrated with as much precision and calculation as the predator has put into planning his clear escape. An organized sexual homicide will have multiple scenes: the location of initial contact or assault, the scene of death, and the body disposal site. This offender is socially adept and may con or persuade his victims into going with him willingly.
http://psychautopsy.weebly.com/organized-vs-disorganized.html
I've included the link above (and the text included in it) only because it offers just one of many similar definitions of an organized SK. Most offer the same generic definitions.
Of the definitions that I've read most, if not all, include something along the lines of: “With organized offenders, there are typically three separate crime scenes: where the victim was approached by the killer, where the victim was killed, and where the victim’s body was disposed of.”.
In this case the location behind the Golden Key offered a remote location where he could get in quickly, dispose of the body and make an equally quick exit back onto the BHP. Once the bodies were discovered, LE was ALL OVER that site searching for anything of forensic value. Yet, as far as anyone knows, they came up empty. This guy clearly planned his escape for when things got hot.
Killing four women behind an occupied motel and then removing shoes, jewelry and all associated items belonging to the victims would seem, to me, to take considerably more time than this guy would be willing to risk. Not to mention the easy access to the BHP should, god forbid, one of his victims manage to slip his grasp.
For this guys purposes a kill site needs to be much more private. A site that is not to far from the location of where he first encounters his victims on Pacific Ave. A site, less than a 5 minute drive, that he can pull into before the bells & whistles go off in his victims head. A site that he has very carefully selected and that he has become intimately familiar with during his planning stage.
That creek that you make note of on Riverside Dr. is actually an inlet that's attached to a waterway that quickly runs into the Atlantic Ocean. A body placed there might stay submerged for while before washing up on the beach in front of The Showboat Casino.
There's a banner ad for The Killing Season above most threads on this topic. That image is exactly how I envision the scene that occurred four times behind the Golden Key. Organized killers are very difficult to apprehend because they go to inordinate lengths to cover their tracks.
Just my opinion.