A man has unexpectedly pleaded guilty in the samurai sword stabbing and bludgeoning deaths of a woman, her two children, her boyfriend and a NASA scientist in Los Angeles County.

Forty-four-year-old Steve Kwon pleaded guilty Thursday as a jury was being chosen for his trial in the 2008 Quartz Hill killings.

Prosecutor Beth Silverman said Friday the plea came as a surprise and that Kwon didn't have anything apparent to gain by admitting guilt. He would have faced up to life in prison if a jury convicted him, and he still faces life after the plea.

Kwon's attorney, David Sakata, declined comment.

In February, the ex-husband of the woman killed also pleaded guilty in the case, agreeing to testify against Kwon, his best friend, to spare himself the death penalty.