From what I gather, the suspect prof did give a sample in the end, and as I say, he was a suspect, along with others, including a cop, so there's quite a mix there.
The info out in public is that the DNA found at the murder scene was Asian, letting all the farang suspects off the hook, but who knows, maybe one of them was complicit in the crime, as at least two persons were spotted "hovering" around the Aree guest-house at the supposed time of the murder.
Then we have a member of the Thai Tourist police who was also under suspicion, apparently a friend of the professor.
I dunno, it's a messy case, and I for one think there's a cover up going on, that the perpetrator is already known to police, and that the situation is highly embarrassing .