I got the impression that the writer wanted the reader to make that connection. Yes.
Oookay, lets just get this thing a little back down on the ground again. First thing, the reference to Fieldnote's post about the odds of two SKs in one area:
In fact, there are only a few cases known, where only one SK is in an an area. The Hillside Stranglers crossed paths with Alcala with the the result, that Alcala dropped a body right on the backside of the same hill which was on the front side dumping grounds to the Hillside Stranglers. To make the chaos complete, a little more on the side of the same foothills, a road led up to some pricey big houses of actors. Guess what, that was where the Manson Family killed.
Or another example: Not only killed William E. Cosden a girl (one out of three, which makes him pretty pale in comparision), he killed her also in a time, Ted Bundy was around there. Neither Bundy nor Cosden knew, but Cosden was pretty happy that Cathy Devine was counted for more than 20 years on Bundy. Saved his life in a way or he would maybe have been a candidate for the needle.
Speaking of Bundy. Bundy tended to drive around in his Volkswagen Beetle. The bug needed gas and Bundy used always the same gas stations, for example one in Golden. One day, and less than an hour after Bundy left, another SK snatched the girl working at exact that gas station. Given, that in thirty miles radius two more girls disappeared from gas stations, witnesses two times described a truck ... well, a serial. How could he know his more infamous college had just filled his car there. Dooh! And so it goes on and on. Rifkin and Alcala overlapped in NYC. Toole, Lucas, Shore and half a dozen others hunted in the Houston area at the same time. Lets face it, it is NOT unusual to have more than one, it is unusual to have ONLY one.
Second thing: A writer's mind
I don't write screenplays, I write novels. So, I am not entirely the same species, only closely related. And the demands, readers, publishers, TV producers and whoever else in that business pose to writers are simply the same lately. A lot of people think, the more brutal, the more disgusting a work is, the more intense it is. And the more intense it is, the more it sells. I got manuscripts rejected by editors back with the comment "not brutal enough". And the business became shallow in that aspect. Thirty years ago, in Manhunt, Thomas Harris came through with descriptions of bloody crime scenes. All what happened played basically out in the reader's imagination. Today, he wouldn't. People demand explicit brutality. And on stage or even worse in TV, both are visual mediums, it goes more and more splatter. Some writers follow the trend, others not so much.
However, writers are a wide variety. From Harris, who wrote one of the most scaring SKs ever, but is happy to hide from people and whip very normal things up in his kitchen (hobby cooks are not that rare under writers) to that guy in Mexico, who wanted to write a cannibalistic vampire and for research reasons, killed some people to eat parts of them and drink their blood. Most however, don't kill. Writers create brutality in their imagination and they do it excessively. That doesn't mean, for most writers, we do it for real. We don't need to. Because while we write those stuff, we have more than our share of scary brutal thoughts. And most writers I know, feel after writing that kind of work rather the need for a shower, good music and a beer or the dark urge to cook something (which usually not cooked from human ingredients, just to make that point clear). So yes, even the most peaceful writer on Earth is probably able to write something disgusting, brutal and utterly vulgar if it is demanded. And admittedly, I wrote some nasty things too. That doesn't make me a serial killer, just a writer. Part of the job is to shock, to shake the reader.