A Douglas County judge on Friday sentenced a 20-year-old Lawrence man to serve more than three years in prison for his role in a September robbery at a south Lawrence apartment.

District Judge Peggy Kittel followed a plea agreement between two parties and sentenced Christopher D. Self to serve 38 months in prison total for his no-contest pleas in the robbery and for violating his probation in three prior cases.

Self in March pleaded no-contest to aggravated battery and conspiracy to commit robbery. Prosecutors said Self drove four co-defendants to the apartment after his brother, Joshua Self, had visited the apartment at The Exchange, 3100 Ousdahl Road, the night before and believed the residents had high-grade marijuana that could be stolen.

Prosecutors allege the defendants were armed with a BB gun and that one victim was knocked unconscious from a head wound.

“He took part in a carefully planned, premeditated, violent robbery, where the victims were truly harmed,” assistant district attorney Mark Simpson said.

Kittel sentenced Joshua Self, 18, in March to serve three years in prison. Another co-defendant, Douglas Bittinger, 20, still has a case pending.

Kittel said Christopher Self would get credit for the more than 220 days in jail he has already served after his Sept. 7 arrest. She ordered him with defendants to pay $1,800 restitution in the case.