Investigators are poring over reopened patient records in two states following the arrest of a nurse with a checkered career who told police he fatally drugged up to 40 terminally ill people under his care.

Charles Cullen, 43, told authorities he administered drug overdoses to put "very sick" patients out of their misery over the last 16 years in nine hospitals and a nursing home in New Jersey and Pennsylvania.

"The evidence that we have indicates that may very well be the case," prosecutor Wayne Forrest said. Cullen was charged with one count each of murder and attempted murder, but more charges could follow.

Investigators are examining records at facilities where Cullen worked as they try to document his claims about the other killings. If Cullen's contentions prove true, it would be one of the biggest hospital murder cases in U.S. history.

During a court appearance Monday, Cullen stood and told the judge, "I am going to plead guilty. I don't plan to fight this." Cullen said he did not want a lawyer, and was held on $1 million bail.

Cullen was charged with murder in the death of a Roman Catholic clergyman who was a patient at Somerset Medical Center (search). He was also charged with the attempted murder of a 40-year-old woman at the same Somerville hospital.

Prosecutors were notified by Somerset Medical Center officials after the hospital fired Cullen on Oct. 31. An internal review had found questionable lab results involving six of Cullen's patients.

Somerset turned over information on the six cases to the prosecutor's office, said Dr. William Cors, the hospital's chief medical officer. All six patients had "multiple, serious medical problems," Cors said.

The charges filed Monday involve the death of the Very Rev. Florian J. Gall, vicar of Hunterdon County in the Roman Catholic Diocese of Metuchen, who died June 28 at Somerset. It was later determined that he had died from a lethal and unauthorized dose of the drug digoxin (search), a heart medication.

The attempted murder charge stems from the discovery on June 16 that a 40-year-old heart and cancer patient had an elevated level of digoxin. The woman recovered from the overdose and was released from the hospital, but died in September.

Cullen had a checkered career and bounced from hospital to hospital. In August 1997, he was fired from Morristown Memorial Hospital (search) for "poor performance," a spokeswoman for the hospital's parent company said.

Cullen worked at St. Luke's Hospital (search) in Bethlehem, Pa., from June 2000 to June 2002, and resigned amid allegations that he had at least twice hidden unopened heart and blood pressure medications in a safety bin for used needles, Lehigh County District Attorney James Martin said.

St. Luke's spokeswoman Susan Schantz said Cullen was immediately removed from contact with patients. The hospital also commissioned an independent cardiologist to review the records of 67 cardiac patients who died in the previous six months. The review turned up no evidence that any of the patients had been harmed.

Schantz said the hospital was never subsequently contacted by anyone checking Cullen's employment references. "Had we been asked, we would have recommended that he not be hired," she said.

Cullen had no record of complaints or any disciplinary actions in New Jersey since he obtained a nursing license in the state in 1987, according to Genene Morris, a spokeswoman for the Division of Consumer Affairs.

Cullen also was licensed to work in Pennsylvania since June 1994, according to the Pennsylvania Department of State. His license was in good standing, officials said.

In Pennsylvania, Northampton County District Attorney John Morganelli said his office is investigating whether Cullen was responsible for the death of a patient at Easton Hospital (search), where he worked for a few months in late 1998 and early 1999.

"We are looking at him, and we are looking at what transpired there," Morganelli said.

Sacred Heart Hospital in Allentown, Pa., 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 had no unsupervised contact with patients.

Liberty Nursing Center (search) in Allentown, said that it fired Cullen for "failure to follow company procedures" after a brief period of employment in 1998. The nursing home said that no harm came to any patients, but that state officials were alerted.

Administrators at Lehigh Valley Hospital (search) in Bethlehem said Cullen worked in the hospital's burn unit from December of 1998 to April of 2000. The hospital said it was examining patient deaths in the unit while Cullen was employed, but had found no evidence of wrongdoing.