One of six defendants charged in the slaying of an Olney man during the robbery of his designer coat last year at the Woodley Park Metro station pleaded guilty Thursday in D.C. Superior Court.

Deon Jefferson, 17, of Landover, who was charged as an adult, pleaded guilty to one count of voluntary manslaughter in the Nov. 17 slaying of 18-year-old Olijawon E. Griffin. Jefferson also pleaded guilty to armed robbery in the attack on one of Griffin’s friends. Both charges carry a maximum of 30 years in prison.

Judge Ronna Beck is scheduled to sentence Jefferson in December.

Jefferson’s five associates are scheduled for trial in September on murder and robbery charges. In March, two 16-year-olds who were charged as juveniles pleaded guilty to armed robbery and lesser offenses in the attacks.

According to prosecutors, Jefferson and his friends had planned a robbery spree in the Gallery Place and Adams Morgan neighborhoods.

Griffin and his friends were in the 1800 block of Adams Mill Road when they encountered Jefferson’s group. Griffin allegedly asked whether he could buy marijuana from them. When Griffin walked with Jefferson’s group to a secluded area, one of Jefferson’s friends pulled out a semiautomatic pistol and pointed it at Griffin. It was Jefferson, according to lead prosecutor Justin Dillon, who removed Griffin’s black Helly Hansen designer jacket.

After the robbery, Griffin returned to his friends as Jefferson’s group ran from the area.

Minutes later, Griffin’s group arrived at the Woodley Park Metro station. There, they saw Jefferson and his friends also waiting for the train. Jefferson, prosecutors say, was wearing Griffin’s jacket.

Griffin and his friends approached the other group and tried to get Griffin’s jacket back. Jefferson’s friends converged on one of Griffin’s friends, beating and kicking him. As the fight continued, Jefferson left and walked away from the fight to another platform area, according to Metro security camera footage.

Griffin tried to intervene as his friend was being attacked. Then, prosecutors said, one of Jefferson’s friends, Chavez Myers, 17, of District Heights, reached over and stabbed Griffin in the chest. Myers has been charged with the most serious count in the incident: first-degree murder.