SONORA, Calif. -- Two brothers accused of kidnapping and killing a man pleaded guilty Tuesday to voluntary manslaughter.

Robert Earl Slawinsky and Paul Curtis Slawinsky were originally booked into the Tuolumne County Jail on charges of kidnapping, criminal conspiracy and murder.

Carl Knight, 23, disappeared in early April, but his body was never found.

In a plea deal, the district attorney dropped the murder charge for each brother in exchange for a voluntary manslaughter charge.

The brothers admitted to county investigators that they had dumped Knight's body over a guard railing into the lake.

Detectives think Knight was hurt in a fight on April 6, which may have stemmed from slashed tires, the Tuolumne County Sheriff's Department said.

Investigators from the department searched for Knight near Jacksonville and Lake Don Pedro.

Knight's family then hired a search team from Idaho to look for the body at a cost of more than $30,000.

"Dispose of the body, and there will be no evidence to prove a second-degree murder. I don't believe this was the heat of passion, I don't believe it was a fair fight," the victim's mother, Debra Knight, said outside of court.

The Slawinsky brothers will be sentenced on Aug. 11. They face a maximum of 11 years in prison.