I'll toss a wet blanket.
The UID appears to be in Alcala's LA apartment in his last stint out there, just before his arrest. His girlfriend at that time was photographed in front of the same sheet exhibiting the same sags and wrinkles. It's 4-5 years after Rachel's Texas disappearance.
Because three girls disappeared at once in that Texas case, what would be an improbable scenario connecting them (or ONE of them) with Alcala vanishes into a well-nigh impossible one. Texas law enforcement believes the girls "left the mall willingly with a person that they trusted," then were "harmed afterward." (That is, molested and murdered, probably within hours.)
It's easy to see where they're getting this. It's hard to forcibly abduct three girls at once without drawing any attention. One is hard. Three figures to be more than three times harder than one. Because it's almost the only way it could happen, they must have got quietly into a vehicle. They took an invitation that they quickly regretted.
It should also be a lot harder to keep three abductees for a long time. There have been a few instances of kidnapped people resurfacing after years. It's a tiny percentage of cases, though, and I don't know of any instance in this category where more than one person was abducted. Three is probably too many. Sooner or later someone's going to sneak away and start making phone calls, or walk into a police station, whatever.
There's also no way to pursue this short of Alcala talking. No bodies. Nothing to match beyond what's been discussed already. No next step to investigate.
Can't prove it's impossible. You can think up a story line where it happens. But it didn't.