BOULDER, Colo. -- A Boulder County teenager who pleaded guilty in the slaying of his girlfriend's mother was sentenced Tuesday to 40 years in prison.

Eighteen-year-old Bryan Grove had been charged with first-degree murder, but accepted a deal in November calling for him to plead guilty to second-degree murder in the stabbing and strangulation death of Linda Damm, 52, of Lafayette, Colo.

Investigators said Grove stabbed Damm in a bedroom of her home and then wrapped her body up and put it in her car.

Authorities said Damm's body was left in the back of her car while it was parked in the driveway of her home for weeks before it was discovered by police last February.

An autopsy revealed Linda Damm had been stabbed 18 times in the neck. An investigation revealed Grove and Damm's daughter, Tess, partied in the house while the body decomposed outside.

Before he was sentenced, Grove addressed the court and said he was sorry.

"I apologize for the pain and tears and grief I caused," Grove said. "I lay myself at your mercy and ask for it."

By pleading guilty to second-degree murder, Grove will be eligible for parole after 30 years. Had he been convicted of first-degree murder, he would have been sentenced to life in prison without the possibility of parole. Following his release, Grove will be on five years of mandatory probation.

Tess Damm still faces a first-degree murder charge for allegedly plotting the murder of her mother. Her trial is set for May 12.

Two other teens -- Jared Smith, 17, and Jared Guy, 19 -- have pleaded guilty for their roles in the crime.