Oleg, along with Benjamin Caffrey, were hired by the Koshka Brotherhood to kill Isaak Sirko. Isaak had "made both men rich" in the past, and called Oleg in an attempt to keep them from killing him, hoping that they had some loyalty to their former employer. However, Oleg told Isaak that they had already accepted the contract, and they would be after him. At first, Isaak tries to get Dexter Morgan to help by saying he'll let him live, but when that doesn't work, he has his bodyguard, Jurg Yeliashkevych, kidnap Hannah McKay, threatening to have her killed unless Dexter kills the hitmen. When Dexter agrees to help, Isaak informs him of both hitmen's method of kiling. Oleg prefers to use rifles, which he always buys local to the locations of his hits, killing from far away, whereas Caffrey prefers to kill up close.
Dexter goes to a shooting range, where Oleg is testing out his rifle for the kill. When he lies down on his stomach to take a better shot, Dexter gets behind him, and stabs him in the back while covering his mouth to muffle any screams.
Isaak Sirko - Oleg failed to kill Isaak as he was killed by Dexter Morgan before he could even start his personal search for Isaak. His fellow hitman, Benjamin Caffrey also failed to complete the task.
Not much is known about either hitman. Oleg apparently had a sick mother, since when Isaak called him his first question was "How's your mother?", to which he replied "Good days and bad".
Isaak states the preferred method of kill of both men, Oleg preferring long distance kills with firearms and Benjamin killing up close by any means. Ironically, Oleg is killed by being stabbed in the back, whereas Benjamin is shot from afar by Isaak.
Mickic's weapon of choice is the Savage Model 110FP sniper rifle. He always buys them local to his targets and tests them out at an outdoor shooting range before killing. He states that he has killed sixteen people, but Isaak claims to have hired Mickic more times than he can count, implying that his actual bodycount is much higher.