I wasn't actually aware of the "touch DNA" concept but its quite a controversial topic:
https://www.creators.com/read/michelle-malkin/01/17/forensic-nightmare-the-perils-of-touch-dna
Not only that, actually doing touch DNA is more expensive than conventional DNA testing:
https://www.ifscolorado.com/touch-dna/
The problem is that Tevin works at the place, which means his fingers would've touched shit.
Because no one died, I really doubt the police has put up a task force to investigate some woman's drink which was most likely accidentally tampered with.
This isn't some high profile murder case with a crack forensics team working around the clock. That's exactly why the detective was sperging trying to get him to confess, because he knows that there's likely no real evidence they're ever going to find.