Mills, Herrmann and others in “Unfinished Business”

So what's the deal with the Lieutenant and the guy from IAD.

Bad history. They went through the academy together and there was an incident...

What kind of incident?

Mouch

The kind that ends with Griffin getting his face punched in.

Why did the Lieutenant hit him?

Mouch

He was talking trash about Casey's family. [Herrmann looks at him in surprise] Um, but...see, we don't talk about that.