Last Wednesday was Virginia state trooper Mark Cosslett's day off. But a sniper was at large, so he came in anyway, patrolling the highways on his motorcycle and stopping at his young son's school to try to reassure the nervous children.

Cosslett, 40, was busy with paperwork about 5:30 p.m. when a call came in that gunshots had been fired. Police said Cosslett was on his way, cruising along the shoulder of Interstate 95 in Springfield, when a truck veered into his motorcycle, killing the 16-year veteran.

Yesterday morning, Cosslett's family, friends and hundreds of police officers took comfort in the details of Cosslett's last day as they gathered for his funeral at Immanuel Bible Church in Springfield.

Under a steady rain, rows of police officers from the Washington region -- and from places including California, Pennsylvania and New York -- lined the front of the church, standing at attention as the flag-draped coffin arrived. Cosslett's widow, Leslie, wore her husband's leather police jacket, pulling it tightly around her against the chill.

"Mark was a hero even before this tragedy, just look at his life that day," said Virginia Secretary of Public Safety John W. Marshall, a former state trooper who was a friend of Cosslett's. "Mark was the most well-known trooper among other law enforcement in the area. The motto of the Virginia State Police, to be helpful to others, was his way of life."

Cosslett, who grew up in Chesterfield, Va., enlisted in the Marine Corps after high school and went on to serve in North Carolina and then Japan. He joined the state police in 1986, where he worked as a motorcycle officer and undercover in the narcotics division.

Troopers said Cosslett was widely known in Northern Virginia's law enforcement circles for his expert handling of the motorcycle, his love of the job and his quirky sense of humor. He would lighten up courses he taught on "outlaw motorcycle gangs" by bringing his Harley-Davidson to class and riding it right out the door.

"He wasn't a stuffy person," said state police spokeswoman Lucy Caldwell. "He was a lot of fun."

Cosslett, who also is survived by two children, ages 2 and 3, was known as a devoted husband and father. When his son was born, Marshall said, Leslie Cosslett moved to a twin bed in the baby's room so her husband could sleep uninterrupted. But Mark Cosslett couldn't stand being away and soon joined them with a sleeping bag.

"Leslie, Trevor and Meghan were Mark's life," Marshall said. "He loved them with all of his heart and soul."

David Gambale, a member of the Boozefighters motorcycle club, said there's no doubt that riding was Cosslett's other passion. He said he'll treasure the memories of taking off with Cosslett and other bikers for their monthly rides.

"He was a good man," Gambale said. "Mark loved to ride. His heart and soul was in it."

After yesterday's service, more than 200 motorcycle officers escorted the family to Quantico for Cosslett's burial.

Police said Cosslett was on the right shoulder of Interstate 95 near Backlick Road on Wednesday evening when a tow truck apparently swerved onto the shoulder after coming upon slow-moving traffic. The truck driver, Forrest Queen, 30, of Dumfries was charged with reckless driving.

Cosslett's death is the first of an on-duty Virginia trooper since 1999. Daniel Lee Williams, 38, died of severe burns two days after his car caught fire as he chased a driver who apparently was trying to evade a sobriety checkpoint in Cumberland County.

Law enforcement personnel salute as the hearse carrying the body of Mark Cosslett, a Virginia state trooper, leaves Immanuel Bible Church in Springfield.Mourners leave the church after the funeral, which was attended by hundreds of officers.