Suspense is important even in cozy mysteries; it provides momentum for the story and comes in especially handy at the climax of your novel. Would your book be as interesting if, after your sleuth names the killer, he's quickly and easily arrested by the police? Yes, there's satisfaction that the detective--amateur or professional--solved the crime and that the murderer has been detained, but it's not exactly riveting reading.
Troy suggests isolating your protagonist (in most cases your detective) to create suspense. He points out the problem facing all writers--how to put the protagonist in a dangerous situation without making him or her look foolish for being in it.
The entire article is interesting, and I really recommend it for anyone looking for ways to make their novel more exciting. Here are some of Mark Troy's ideas for isolating your detective (believably) with the murderer:
Have your detective confronted while he's out gathering evidence.
Have your detective isolated with the killer while he's in a remote setting.
Have the killer turn out to be a mentor or friend of your detective.
Have your detective eagerly run ahead of his backup and end up in the killer's clutches.
Troy offers many other ideas for adding suspense, too--some of them involving internal isolation techniques--so be sure to check it out. I thought it was a fresh perspective on an old plotting problem.