NEW BRITAIN, Conn. — A judge entered not-guilty pleas Monday on behalf of a former drifter charged in the slayings of six people in Connecticut in 2003 during what authorities called a serial killing spree involving a van he called the "murder mobile."

A hearing in the case against William Devin Howell was held in New Britain Superior Court. The native of Hampton, Virginia, also waived his right to a probable cause hearing where prosecutors would have to show there's enough evidence to proceed to trial.

Howell, 46, already is serving a 15-year prison sentence for manslaughter in the killing of 33-year-old Nilsa Arizmendi of Wethersfield. She and the six other victims — five women and a man — were killed in 2003 and later found buried behind a shopping center in New Britain.

Howell sexually assaulted three of the women and kept one of the bodies in his van for two weeks, sleeping next to the body and calling the victim his "baby," according to an arrest warrant affidavit. Howell also told a cellmate "there was a monster inside of him that just came out" and described himself as a "sick ripper," according to the warrant.

New Britain police say Howell was mowing lawns and working other odd jobs in Connecticut at the time of the killings.

The other victims were identified as: Joyvaline Martinez, 24, of East Hartford; Diane Cusack, 53, of New Britain; Mary Jane Menard, 40, of New Britain; Melanie Ruth Camilini, 29, of Seymour; Marilyn Gonzalez, 26, of Waterbury; and Danny Lee Whistnant, 44, of New Britain.