Castor Troy: You'll be seeing a lot of changes around here. Papa's got a brand new bag.
Castor Troy: If you dress like Halloween, ghouls will try to get in your pants.
Dr. Walsh: What do you want?
Castor Troy: Take one goddamn guess!
Castor Troy: Lies, deceit, mixed messages... This is turning into a real marriage.
Castor Troy: I hate to see you go, but I love to watch you leave.
Castor Troy: It's like looking in a mirror. Only... Not.
Pollux Troy: Seeing that face on you makes me afraid my tiramisu might come back up.
Castor Troy: Well, think about me. This nose. This hair. This ridiculous chin.
Castor Troy: You're not the only one in the family with the brains.
Pollux Troy: No, although now I am the only one with the looks.
Castor Troy: Touche.
Castor Troy: No daughter of mine would shoot so wide.
Castor Troy: Well, I've gotta go. I've got a government job to abuse, and a lonely wife to fuck. Oh, sorry. Make love to.
Chosen answer: Although they were on the same side, Troy is currently posing as Archer, which means he would have to do everything that the FBI would expect Archer to be doing. The whole point of the raid was to take out Archer, as well as Troy's gang. He would have rather risked killing part of his own gang than risk exposing his identity to anyone else.
Casual Person
That doesn't really make sense. In the scene, he goes out of his way to shoot him and smiles while doing so, carefully and slowly. Was not a collateral damage situation. The question is why he deliberately goes out of his way to kill him.