I am moderately skeptical of the story that it was the fingerprint alone which led them to the kidnapper, and I am curious for more details. I have a vague suspicion the police had a pretty good idea of who they were looking for already, and while the fingerprint confirmed it, eventually they would have picked the same guy up. The existence of the fingerprint allows them to keep other sources and methods discreet.

That being said I'm not implying that the cops did anything illegal or even untoward. And further if this goes to trial the defense is certainly entitled to the full story, but it seems likely this guy will plead guilty and we might not know for years why the cops came to look at this guy.