Newark, N.J ? A former nurse who claims to have killed as many as 40 patients over the past 16 years was fired from at least two hospitals and was even the subject of a murder investigation. But Charles Cullen kept managing to land another job.

Authorities say the case underscores serious flaws in a system in which hospitals report only limited information about nurses to other prospective employers for fear they might get sued. A severe nursing shortage also may have played a part.

“Short of an actual conviction for a criminal act, there is nothing that needs to be reported when someone is fired,” said Dr. William Cors, Somerset Medical Center’s chief medical officer. “That needs to change.”

Cullen, 43, is charged with murdering a Roman Catholic clergyman and attempting to kill another patient at Somerset Medical Center. More charges could follow after prosecutors complete their investigation of Cullen’s claims that he killed 30 to 40 patients at nine hospitals and a nursing home in New Jersey and Pennsylvania.

Prosecutors said he gave the seriously ill patients lethal drug overdoses to end their suffering.

Despite Cullen’s spotty record, officials at Somerset had found nothing wrong after checking his credentials. That is because most hospitals will only confirm the dates of employment for a former worker, and will not make a positive or negative recommendation.

Donna Leusner, a spokeswoman for the state Department of Health and Senior Services, said hospitals were only required to report to the state agency suspicions of criminal activity that endangers the lives of patients or employees.

Cullen worked at and was fired from several hospitals in Pennsylvania.

At St. Luke’s Hospital in Bethlehem, Pa., where Cullen worked from June 2000 to June 2002, Cullen was removed from patient contact after two unopened heart medications were found hidden in a hypodermic needle disposal bin in June 2002. He quit rather than cooperate with the inquiry, hospital spokesman Susan Schantz said.

Simultaneously, a nurse at the hospital complained to prosecutors that she suspected that Cullen had been involved in “inappropriate medication of patients,” according to Lehigh County, Pa., prosecutor James Martin. Authorities reviewed the records of 67 patients who died in the coronary care unit in the last six months of Cullen’s employment but found no evidence of wrongdoing.

Martin sent a letter to the hospital on May 28, informing it that the investigation was closed.

The nationwide nursing shortage also may have helped Cullen get so many jobs. Hospitals and other health care institutions compete fiercely for nurses, offering cash bonuses and even recruiting overseas. More than 30 states are grappling with a shortage estimated at 136,000 nurses.