Somerville, N.J. ? A former nurse who claimed to have killed as many as 40 patients by giving them lethal doses of intravenous drugs pleaded guilty Thursday to 13 murders in a deal that will spare him from the death penalty.

Charles Cullen, 44, also admitted to two attempted murders and agreed to plead guilty to a 1998 murder in Easton, Pa.

He will also cooperate with authorities as they try to uncover other crimes he may have committed between 1984, when he entered nursing school, and his arrest last Dec. 12.

In an hourlong court hearing Thursday, Cullen wore a bulletproof vest under his sport shirt. He showed little emotion and uttered few words beyond saying, “Yes, your honor,” and giving the names of the drugs he used in the 13 murders and two attempts — all last year at Somerset Medical Center.

He spoke up twice to correct defense lawyer Johnnie Mask, once to clarify that one crime was an attempted murder and not a murder, and once to say a victim was a man, not a woman.

Authorities said they would question Cullen about suspicious deaths in the nine hospitals and one nursing home where he worked over his 16-year career. Authorities would not speculate on how many deaths Cullen may have been responsible for altogether, but New Jersey Atty. Gen. Peter Harvey said that the 40 Cullen claimed after his arrest were not impossible.

Cullen agreed to plead guilty to all the murders he committed, and prosecutors in New Jersey and Pennsylvania expect more guilty pleas in both states.

He is to be sentenced eventually to multiple life sentences in each state and, according to the plea deal, will serve prison time in New Jersey.

In exchange for Cullen’s help, prosecutors agreed not to seek the death penalty against him for any murders in five counties in New Jersey and two in Pennsylvania.

New Jersey authorities said he would not be eligible for parole for 127 1/2 years.