As doctors at Cooper University Hospital desperately tried to save Sean Cullen's life Monday night, dozens of his fellow New Jersey state troopers waited anxiously in another room, holding out hope that he would survive.

Cullen, a high school and college wrestling star from Cinnaminson who had long dreamed of becoming a state trooper - and who graduated from the academy in August 2014 - was struck by a car while walking next to an earlier accident on I-295 in Gloucester County.

At Cooper, Cullen's father, Eamonn, learned that the troopers had gathered and walked downstairs to speak to them, said Col. Rick Fuentes, superintendent of the state police, who was at the hospital.

"He lived the dream," Eamonn Cullen told the troopers, according to Fuentes. "This is what he wanted to do."

Cullen's death just after 12:30 a.m. Tuesday, about four hours after the accident, sent shock waves through the schools, wrestling teams, and police forces where he had garnered accolades, and was known for his drive and good humor.

Cullen, 31, was the third state trooper to die in the line of duty in 10 months, following Eli McCarson and Anthony Raspa, who also died in car accidents.

"The mood is devastating," Fuentes said Tuesday afternoon. "A tragedy like this is not something you can ever get accustomed to."

Authorities said Cullen suffered severe head injuries in the accident in the southbound lanes at Milepost 23.4 in West Deptford Township. The 22-year-old driver of the car that struck him stopped immediately. Authorities said she was cooperating with investigators and had not been charged.

Cullen had a fiancee and a 9-month-old son, and his older brother, Garrett, is a state police detective.

Besides his father and brother, Cullen is survived by his mother, another brother, and a sister.

Outside one of the family's Cinnaminson homes Tuesday, Cullen's father tightly embraced police officers from Westampton Township, where Cullen worked before he became a trooper. The family declined to comment.

At Cinnaminson High School, where Cullen was captain of the wrestling team and the first wrestler in school history to reach 100 wins, principal Darlene Llewellyn announced Cullen's name on the loudspeakers and requested a moment of silence. Flags were put at half-staff.

"Cinnaminson lost one of their own," Llewellyn said.

Gov. Christie expressed condolences to Cullen's family in a statement.

"Every day, the men and women of the New Jersey State Police put their lives on the line to protect our citizens," Christie said. "The sudden and tragic loss of New Jersey State Trooper Sean Cullen reminds us how fragile life truly is and the dangers police officers face daily on the job."

Cullen was born in 1985 in Dublin, Ireland, and came to the United States three years later. He grew up in Cinnaminson.

After graduating from high school in 2003, and earning the title "Class Chatter-box" in the yearbook, Cullen attended Lycoming College in Williamsport, Pa.

His wrestling coach, Roger Crebs, had recruited Cullen there after witnessing the young man's drive in high school matches.

"He's the type of kid that he had a goal in mind, and he knew what he needed to do to get to those goals," Crebs said.

Cullen lived up to the hype. He was named an all-American his sophomore year, served as team captain his junior and senior years, and finished with a 94-30 record. He was later inducted into the Lycoming Athletics Hall of Fame.

Cullen graduated with a bachelor of arts degree in criminal justice. He began his law enforcement career in Sea Isle City, N.J., where he worked two summers. His former colleagues there remembered him on Tuesday with a Facebook post memorializing his badge number - 1250.

After Sea Isle, he joined Mount Holly's police force, where he worked as a part-time officer from April 2007 to February 2012.

Cullen took every assignment that came through the door, Mount Holly Police Capt. Richard Spitler said, and often worked extra hours beyond his 6 p.m.-to-midnight shift.

"He loved his job," Spitler said. And he made his aspirations known, he added. "His dream was always to be a state trooper, and we were proud when he finally fulfilled that dream."

Cullen, a member of the 154th state police class, graduated Aug. 29, 2014. He was assigned to the Buena Vista and then Bellmawr stations.

On Monday, Cullen was working the 6 p.m.-to-6 a.m. shift when he was dispatched around 8:15 p.m. to a car fire from an earlier crash in the southbound lanes of I-295. A West Deptford police officer and Cullen were working at the scene when Cullen was struck, Fuentes said.

State troopers and other authorities rushed to the scene, then to Cooper.

Fuentes said he was with the family when doctors told them their son could not be saved. He then walked downstairs with his commanders to inform the waiting troopers, who had heard about Cullen's dream from his father.

The hugs and tears came quickly. A young trooper's life, a dream, cut short.

"Sean was really at the beginning of his career," Fuentes said.

Funeral arrangements had not yet been made Tuesday afternoon.

mboren@phillynews.com

856-779-3829 @borenmc

Staff writer Dana DiFilippo contributed to this article.