Pard was an undercover G-Man!

Well, "G-Dog" anyway, or at least some sort of law enforcement officer.

Think about it - he contrives to be present during the robbery. He doesn't prevent the robbery or arrest anyone because he wants to get the entire gang. Later, he accompanies Earle when he plans to visit Big Mac but instead has to shoot Kranmer (how else would the cops have tied Earle to Kranmer so quickly if Pard hadn't tipped them off???). He then learns all about "Doc", and he even checks out Velma and her family to make sure they have nothing to do with the crime. And finally, he leads Earle right into the sights of the police sniper.