Det. Diaco seems to be the 5th wheel

I like the actor a lot, was hoping he'd have a good character but I had a weird hunch somehow that he'd be useless the first time he opened his mouth. Now it's pretty clear he is but he seems really likeable and I actually look forward to seeing him plus he's so brief unlike the usual filler in crime shows. It's hilarious how his job is literally just filling in some minor details and delivering some line about how he can bootleg tickets to the Knicks game or designer kitchen towells at half price.

I'm a bit confused though, does he actually live in the police station? That scene of him just kicking it on a cot having a beer was so abrupt and unexpected I thought maybe I missed something LOL

My only guess is he was partnered with Owen, and Clark got shoved down their throats by the PC without an actual need for another detective. Owen gets tasked with training the new guy, and Diaco is left to do whatever needs doing. It does look a little painful at times with this guy having no one to talk to (his "big" scene so far was the brief conversation with Arroyo in the bunk room).

5th Wheel indeed. Diaco seems to be as much the precinct concierge as the first detective on the crime scene outlining the known facts to the others as they arrive.

He seems strangely neutered for a guy of his physical stature, which has the effect of distracting me in very scene he is in. He reminds me of Biff, from Back to the Future, after Marty returned to the now-altered present from 1955.

He does, but I like it that way.

He's a good guy to have around, and his research seem to be very important to the cases. Why he doesn't have a partner, I really have no idea, I don't really see the logic in it, but IF he did, he wouldn't be working with the others.
Two teams on one case is enough, three is just a waste.

Like Captain Brass in early CSI, he's there to provide exposition.

He tells the viewer who the victim is, how the murder was committed, what the background check revealed, whose alibi checked out, etc.

Perhaps, like Paul Guilfoyle, he'll get a larger role as time goes by.

I see him as the Profaci (Law & Order episodes circa 1990-98) of the squad. Does some legwork, gets a few lines.

Raylan Givens: You make me pull, and I'll put you down.

Yes, small and forgettable part.