Lukas Berzai is a Disavowed Scorpian. In Battlestar Libra he was one of the mercenaries aboard the rogue destroyer Deimos when it encountered the Libra fleet in Episode 21 - The Enemy of my Enemy. Lukas was among those who pledged their knives to Scott Duncan and became part of the Spectres. (He did not specifically appear by name in this episode.)
Lukas had been a sniper in Rattler's Sons of the Devil mercenary battalion. In Libra Episode 29 - Best Defense he was teamed with Nikol S'Jahar as a sniper spotter. This is an ongoing special assignment and the team can function with either the Marines or the Spectres.
The crime for which Lukas was disavowed has not been specified within Battlestar Libra. Lukas bears a tattoo across his left eye as the mark of Disavowal. His tattoo has been lightened, though it is still visible.