MARTINEZ -- A pair of El Sobrante brothers were sentenced to prison Monday in connection with the killing of a 22-year-old El Sobrante man nearly six years ago, a case with still-unanswered questions that led to a plea deal for the two gang members.

Nathan Wardley was fatally shot on Dec. 6, 2007, at Argyle Road and Kirkpatrick Drive in El Sobrante, a block from his house while dressed in pajamas.

On what would have been Wardley's 28th birthday Monday, 21-year-old Jason Kent pleaded no contest to assault with a deadly weapon resulting in death and was sentenced to five years for Wardley's slaying. His brother, Thomas Evans-Kent, 24, pleaded no contest to voluntary manslaughter, and to assault for attacking a man in Pinole in May 2007, and was sentenced 15 years. Both brothers admitted to doing their crimes for the benefit of a criminal street gang.

Assistant District Attorney Tom Kensok said authorities don't know the motive for the killing, or whether Kent, Evans-Kent or a third suspect, Brandon Quintana, fired the fatal shots. Quintana, 18, was shot and killed on Interstate 80 in Pinole almost three months later. The brothers were charged with murder for Wardley's death in 2011.

Wardley's family told a judge Monday that they were unhappy with the plea deals for the brothers, but they understood and accepted the prosecutorial challenges in trying the case.

"We're not here to be vengeful or hateful or anything, but Nathan was murdered -- coldhearted, calculated murder -- and you are going to have to live with that," Nathan's father, Ike Wardley, said to the defendants.

Contact Malaika Fraley at 925-234-1684. Follow her at Twitter.com/malaikafraley.