An aspiring rapper who embraced a style of music known as “horrorcore” pleaded guilty Monday to killing his 16-year-old girlfriend, her parents and her friend.

Richard “Sam” McCroskey was sentenced to life in prison Monday as part of his agreement to plead guilty to two counts of capital murder and two counts of first-degree murder.

His attorney, Cary Bowen, said after the hearing that the prospect of the death penalty was a major factor.

“Four bodies are pretty compelling evidence,” Bowen said. “This is the kind of stuff that citizens any place in this country are terrified it could happen to them. This is the kind of case death penalties arise from.”

McCroskey, from Castro Valley, Calif., arrived at the Prince Edward County Circuit Court shackled and heavily guarded. He showed little emotion during the hearing and offered simple “yes” and “no” answers to questions from the judge.

McCroskey pleaded guilty to killing his girlfriend, 16-year-old Emma Niederbrock; her parents, Presbyterian minister Mark Niederbrock and Longwood University professor Debra Kelley; and Emma’s 18-year-old friend, Melanie Wells of Inwood, W.Va.

Family members of the victims sobbed softly during the hearing. They left without speaking to reporters, but issued a written statement: “We have endured a tragedy of unspeakable proportions. We are relieved that justice has been done.”

Prosecutor James R. Ennis revealed that the women were bludgeoned with a wood-splitting tool while they slept on Sept. 18, 2009. Mark Niederbrock was killed with the tool when he came to check on them. Ennis declined to speculate on a motive.

McCroskey and Emma Niederbrock shared an interest in “horrorcore” music, which sets lyrics about rape, murder and mutilation to hip-hop beats. Bowen said the music had nothing to do with the killings.

McCroskey, a Web site designer and music promoter, had been rapping under the name “Syko Sam.” He flew to Virginia to visit Emma, and her parents drove them and Wells to a horrorcore music festival in Michigan Sept. 12. Police found their bodies six days later after Wells’ parents became worried that she didn’t return home.