SF short story about a shapeshifter serial killer and a police detective (who we learn later is also

I'd say it's been at least fifteen years since I've read it.

The main character is presented as a normal police detective, investigating/following a serial killer known for leaving his victims as savaged corpses.
I believe he tracks him down to some warehouse, and the killer taunts him for a while, and when they meet, the killer turns out to be some shapeshifter who takes on the form of monsters. The detective remains unimpressed, and after they fight for a while, he reveals that he is a shapeshifter as well, and a far more experienced one, too.
He kills the other one by taking on an amorphous form, completely enveloping the other and suffocating him that way.

That description sounds familiar to me, and I might I might have read it too. Let me see if I can think of the the title or any details. Hmm...

Huh, found it:
It was Hardshell, by Dean Koontz.

Huzzah!

touchstone fairy Hardshell

Short stories are always harder to find it seems - for anyone interested, this story is also in Strange Highways which was released as a MMP in 1996.