Kaplan

Tech Sergeant Kaplan is a corrupt UNATCO soldier. He keeps enemy weapons and items and sells them to anybody that's willing to buy them.

Sam Carter knows of Kaplan's corrupt nature, but is more focused on whomever is breaking into the UNATCO armory and stealing sensitive equipment.

In-game
Kaplan can be found near the UNATCO compound during the first mission. He has a scope mod for 700 credits, a box of 10mm rounds for 200, and a box of Tranq Darts for the Mini-Crossbow for 60. The scope mod is extremely useful, especially early in the game, so get it from him as soon as you can. You probably won't have enough money to buy one from him, so wait until you get paid by Manderley, then get it.

If you attack or kill Kaplan, nobody seems to care.

Kaplan disappears after you leave Liberty Island for the first time.