I'm looking for a novel or short story that I read in the late 90s or early 2000s; I remember that it was from the point of view of a detective or cop who was tracking a serial killer.
The protagonist was a member of a secret species of shapeshifters, and chose to live as a human. When he found the serial killer, he discovered that it was another member of his species--but young and psychotic.
Since his species can regenerate from any injury, he defeats the murderer by shifting himself into a fluid form and perfectly enveloping him until he suffocates--a tactic that is only possible because the protagonist is relatively old and experienced with his abilities.
And that's all I remember about it. The aspects I remember result in such generic search terms that I haven't had any luck with Google. I suspect I might have read it in an anthology, or perhaps in a magazine like Asimov's.