Lakewood, N.J. - A man was being questioned by a police officer who had driven up to him on a residential street Friday afternoon when he pulled a handgun from his clothing and fired three bullets into the officer in what the county prosecutor called "a heinous, execution-style killing."

A massive manhunt was under way in this community near the Jersey shore for the killer of Patrolman Christopher Matlosz, who had just transferred from the midnight shift a week ago and was engaged to be married next year.

His fiancee rushed to the hospital, where he was pronounced dead less than an hour after the shooting.

"This is a terrible tragedy, and our hearts and prayers go out to Officer Matlosz's family, friends, fellow officers and the entire New Jersey law enforcement community," Gov. Chris Christie said. "While the facts are still being gathered, we support the Lakewood police and Ocean County Prosecutor's Office in their work to bring swift justice to whomever is responsible."

Prosecutor Marlene Lynch Ford said Matlosz never saw it coming. She said the officer was conducting "a routine stop" of the suspect, chatting with him for a few minutes, leading authorities to believe the two may have been acquainted with each other before the shooting.

"This was an encounter that was between the officer and the person, not hostile," she said. "The individual stepped back and suddenly pulled out a handgun and shot the officer."

While the suspect fled on foot, a neighbor called 911 just after 4 p.m. to report an officer down. Matlosz was rushed to Jersey Shore University Medical Center, where he died in the trauma unit. He is survived by his mother and a brother.

The suspect was described as a black male in his early 20s or late teens, stockily built with sunken eyes and puffy cheeks. He was wearing a black hoodie and dark jeans slung so low that gray boxer shorts were visible, according to a witness account to police.

Officers were swarming the neighborhood and several helicopters were swooping low over homes and trees in the area. State Attorney General Paula Dow promised the killer would be caught.

"I am deeply saddened to learn about the fatal shooting of Lakewood police Officer Chris Matlosz, who lost his life in the line of duty this evening," Dow said. "Rest assured, the suspect responsible for this horrific act will be apprehended and brought to justice."

The State Policeman's Benevolent Association is offering a $40,000 reward for information leading to the arrest and prosecution of the suspect, according to the group's spokesman, Jim Ryan.

Matlosz, 27, joined the department Aug. 14, 2006, and had just transferred to the evening shift after more than three years on the midnight shift, police Chief Robert Lawson said.