I actually have some sympathy for the cop here, IF his version of the story is true. He tries to get three guns off the street, and all he gets is grief for it.
Suppose you found a WalMart gift card in the parking lot. So you make the effort, and go back into the store to turn it in. Instead of thanks, the manager begins to hassle you and asks you all sorts of harsh questions. Perhaps you might start swearing. I know I just might.
I know a gift card is not the same as a gun, but still...
As a police officer, he should have known better. If those weapons were previously used in a crime, it would be much easier for detectives to track down the criminals who used them. Turned in anonymously, all they have are the weapons. If the Sgt had turned them in, he could have led detectives to the person who gave them to him. Sounds like he was trying to protect a bro and it backfired.