You'd kinda think that a Texas Ranger would be a little smarter than your average bear. Unfortunately, a lot of these books featuring some nameless bad guy seem to have law enforcement heroes who seem...careless?
Ok, so 10 years ago, an armed robbery took place at the diner the h worked at. She was the only survivor, and it was mostly due to being grazed - head - and the addlepated robber not checking. I never really understood why he made the owner drive to the middle of nowhere and killed him elsewhere. The h's parents split up due to dear old dad not being able to handle this, the h's mom got a legal name change (and was able to continue being a vet. Huh). And they reinvented themselves.
The owner's remains have been found and our H shows up shortly after the h gets a newspaper and finds this out. He wants her to undergo hypnosis to see if she remembers anything. She comments that she'd always sort of had the impression the killer knew where she was but since she didn't seem to remember anything, he left her alone.
Undergoes hypnosis, remembers a detail or three, goes home. Ok yes; sex does happen shortly after the hypnosis, and he stays the night after taking her home, but he leaves her there. No-one to watch her or anything.
The killer shows up at the office she works in. She recognizes the tattoo but keeps her cool until well after he's left (and her co-worker comes back from break). She quickly calls H and tells him. He collects her and takes her to his mountain hideaway (that everyone at the office knows about). And then he decides to set a trap. Of course, they go to the pond unarmed and without a phone. He goes back to fetch and well...
We never learn the ID of the killer - there was some speculation that his brother worked with the Rangers but it's never clarified. And even when he's suspicious that there might be a leak, he doesn't exactly make much effort to cover his tracks. And why, if you're setting a trap, would you ever be unarmed, let alone without the phone?