Former nurse Charles Cullen (search) pleaded guilty Thursday to murdering 13 patients and attempting to kill two others at hospitals in two states as part of a deal with prosecutors to spare his own life.

The pleas were the first from Cullen, who said last December that he had killed between 30 and 40 patients during the 16 years he worked as a nurse at 10 hospitals in Pennsylvania and New Jersey.

Cullen, 44, was charged with a murder and two attempted murders in Somerset County on Dec. 15 and initially said he intended to plead guilty.

But it took more than three months for him to do so, in large part because prosecutors from seven counties had to agree to the details of a guilty plea.

According to the deal, prosecutors will not seek the death penalty, and Cullen will cooperate with authorities in both states.

He faces consecutive life terms for the murders with no eligibility for parole for more than 120 years under terms of the agreement. A sentencing date was not set. Cullen will remain in custody pending sentencing.

Most of the victims' families didn't realize at the time that the deaths weren't from natural causes, because the victims were often seriously ill. Prosecutors have said Cullen claimed he gave the patients lethal drug overdoses to end their suffering.

His admission has triggered at least a dozen lawsuits filed against the hospitals where he worked by relatives of deceased patients.

The case has also raised concerns about hospitals' oversight of medical errors, narcotics security and background checks on prospective employees. Cullen was fired from five hospitals and resigned from two amid questions about his job performance. But he kept managing to land another job.

Cullen's claims also gave lawmakers in New Jersey reason to speed along a bill requiring health care facilities to report medical errors to the state. Gov. James E. McGreevey (search) signed it into law Tuesday.

Legislators said the new law could have prevented Cullen's killing spree, had it been in place.