Lieutenant Grodin is a police officer who made 2 appearances in Season 2 starting with "The Truth About Holly".
Grodin is a friend of Dominic's. From what Caitlin says about him in "Sins of the Past", he is Dominic's regular poker buddy and they play every thursday.
Grodin first appears in "The Truth About Holly" near the beginning. Hawke and Dom have just rescued Holly from the villa of Ed Aarons. Grodin is questioning Holly. Grodin is keen to make a charge of kidnapping Holly stick on Aarons. Aarons, it seems, has a finger in every racket and Grodin would really like to put him away. Unfortunately Aarons has lots of friends in Mexico and the circumstances of the rescue don't make it easy to file for extradition.
He meets Hawke and Dom again, just after Dom's Hughes 500 has caught fire and blown up. Again they are frustrated because there's no sign of foul play and just no evidence to be had against Aarons or anyone else. Hawke and Dom feel they know who did it, but Grodin tells them it is not a matter of what he thinks but what he can prove. Hawke tells Dom not to be too hard on him. "His hands are tied. But ours aren't," he says.
Grodin next appears in "Sins of the Past". He is at the Santini Air hangar waiting for Dominic to return from a flight. Dominic thinks it is a social visit but actually he is there to arrest Dominic for the murder of his ex-wife. At the police station, Grodin tries to be nice to Dominic. Hawke accepts that he is only trying to do his job but Caitlin doesn't think he is doing enough and gives him an earful about the kind of friend he is.
Throughout his appearances, Grodin plays "the straight guy". He is friendly to Hawke and Dominic but always plays by the rules.