A Bethlehem critical care nurse told investigators he killed 30 to 40 patients over the past 16 years and firmly confessed Monday to two charges in a Somerset County courtroom, ignoring a judge's repeated requests to remain silent.

Charles Cullen, 43, who worked at almost every hospital in the Lehigh Valley, was charged with one count of first-degree murder and one count of first-degree attempted homicide in the deaths of two Somerset Medical Center patients earlier this year.

Authorities said their investigation is just starting, but it could become one of the biggest homicide cases ever in New Jersey.

Cullen tried to plead guilty numerous times Monday, but New Jersey Superior Court Judge Paul Armstrong said he was not prepared to accept a plea at an arraignment hearing and repeatedly advised Cullen to remain silent. He urged Cullen to find an attorney or accept a public defender before making further statements.

Cullen, a slim, fit-looking man dressed in prison garb, spoke clearly and lucidly as he told Armstrong he didn't want a trial.

"I don't want to contest the charges. I plead guilty," Cullen said in a courtroom full of reporters from New York to Philadelphia. "I don't want to be represented. I don't intend to fight this."

Cullen, of Fernwood Street, told investigators over the weekend that he committed the crimes by improperly medicating the victims to ease their pain and suffering, according to documents released by Somerset County Prosecutor Wayne Forrest.

"As you can imagine, this is by far the biggest homicide investigation undertaken by the Somerset County prosecutor's office, and maybe by any law enforcement agency in New Jersey," Forrest said at a news conference.

Forrest said charges in a third case are pending autopsy results, but added that Cullen has told investigators he was responsible for 12 to 15 deaths at the medical center during a 13-month period.

Lehigh County District Attorney James Martin called on Pennsylvania State Police to reopen a 2002 probe related to several suspicious deaths while Cullen worked at St. Luke's Hospital in Fountain Hill.

Northampton County District Attorney John Morganelli is looking into a suspicious death at Easton Hospital while Cullen worked there.

Cullen also worked in the burn unit at Lehigh Valley Hospital, Salisbury Township, and Liberty Nursing Home in Allentown. LVH officials said they are re-examining the records of patients who died while Cullen was there but so far have found no problems.

Liberty officials, in a prepared statement, said Cullen was fired for failure to follow company procedures.

Sacred Heart Hospital in Allentown said Cullen worked there for 18 days in July 2002 and was fired for having "interpersonal problems" with other employees. Hospital spokesman Chris Sodl said Cullen was in an orientation period when he was let go, and had no unsupervised contact with patients.

Forrest said Cullen was arrested without incident Friday night after he dined with a companion at a restaurant on Route 22 in Bridgewater. He was alone when arrested, said the prosecutor.

Forrest said his investigation is still in the early stages, and he declined to predict how long it would take to finish. He said investigators are looking at possible accomplices, but downplayed the possibility that Cullen had help.

Cullen, a divorced father of two, graduated from West Orange High School in 1978 and served in the Navy for six years before attending Mountainside Hospital School of Nursing in Montclair, N.J. He graduated from Mountainside in 1987 and worked at St. Barnabas Medical Center in Livingston, N.J., from June 1987 to January 1992.

Cullen went to Warren Hospital in Phillipsburg in February 1992 and was the subject of an inconclusive investigation there related to patient deaths before leaving in December 1993.

The charges in Somerset County come after abnormal blood tests revealed the presence of unusual medication amounts in at least a half-dozen patients who have since died. The tests revealed unusually high levels of the prescription heart medicine digoxin and unusually low blood sugar levels in the patients, Somerset Medical Center officials said last week.