Christopher DiMeo, charged with his girlfriend in three murders and a string of jewelry-store robberies in New York and Connecticut, has pleaded guilty to first-degree murder and robbery in conjunction with the killing of Thomas Renison, 48, owner of J & J Jewels of Glen Cove, N.Y. He will likely be sentenced to life in prison without parole, press accounts said.

DiMeo, 23, admitted to killing Renison during a three-month spree in which he robbed at least four jewelry stores with the help of his girlfriend, Nicole Pearce, 23, and his mother, MaryAnn Taylor-Casey, 41.

Pearce pleaded guilty to first-degree robbery. She is expected to receive a prison term of 20 years.

As part of his plea bargain, DiMeo was promised that a murder charge against his mother would be dropped and that she would receive a 15-year prison sentence, press accounts said. She recently pleaded guilty to robbery charges after admitting to having driven the getaway car.

Pearce and DiMeo face additional charges in Connecticut, where DiMeo has been charged in the slayings of Timothy Donnelly and his wife, Kimberly Ann Donnelly, owners of Donnelly Jewelry in Fairfield, Conn.