Elaine Thompson, Associated Press
The first two of four caskets arrive for a memorial service for four slain police officers at the Tacoma Dome Tuesday.

TACOMA, Wash. — About 20,000 mourners, mostly members of law enforcement from Washington state and across the country, honored four slain officers who were remembered Tuesday as heroes and loving family members.

A procession of 2,000 cars followed the flag-draped caskets of Sgt. Mark Renninger and Officers Ronald Owens, Tina Griswold, and Greg Richards to the Tacoma Dome, where the memorial service was held. Several candlelight vigils have been held for the officers since the shooting on Nov. 29, but Tuesday's memorial service and procession are believed to be the largest in state history.

"I would have gone through any door with Mark and I trusted him with any mission," said Assistant Chief Mike Villa, of the Tukwila Police Department, where Renninger once worked. "I will not forget Mark, the good that he did or the life that he led."

The Lakewood officers were killed by a lone gunman Nov. 29 before the start of their shift. Authorities say Maurice Clemmons singled them out and spared employees and other customers at the coffee shop in Parkland, a Tacoma suburb about 35 miles south of Seattle.

Clemmons was shot to death last week by a Seattle police officer after a two-day manhunt. Prosecutors said he received help from family and friends, and seven people have been arrested.

"Our dad was a hero to many even long before he became a policeman," said Richard's teenage son, Austin. "The way he lived his life spoke volumes."

Lori Lightfoot and Sheila Chandler, both police detectives from Fresno, Calif., were among officers who traveled from as far away as New York, Chicago and Canada for the service. They said the deaths of the four Lakewood officers brought back memories of four Oakland police officers killed during a traffic stop and a shootout in March.

"It's just disbelief," Lightfoot said. "It's unbelievable that it could happen again."

Gov. Chris Gregoire said that the sacrifice would not be forgotten, adding: "We owe the children of these officers, all nine of them, a present and a future that is safe and secure."

Pamela Battersby, a friend and co-worker of Griswold, said Griswold liked dressing up and going out, but that she was also a tomboy rode motorcycles. She met not only the women's standards on physical fitness tests "but the men's as well," Battersby said.

The elder sister of Owens said that her brother followed their late father into law enforcement.

"They were two peas in a pod," said Ronda LeFrancois. "I know they are in heaven together."

Cpl. Jack Hundial, of Surrey, British Columbia, was one of 1,000 Royal Canadian Mounted Police in attendance. He said he and his colleagues wanted to show their support because "it could have been any of us."

"I think about their families," he said. "I don't think you ever find true closure for something this tragic."

Floral arrangements lined the stage at the sports arena, as well as two motorcycles, a drum set and a NASCAR race car. Griswold and Owens both loved motorcycles, Owens played the drums, and Renninger was a big NASCAR fan, according to Lakewood Mayor Dennis Fountain.

The service included a 25-minute photo slideshow of the officers. It ended with a bell rung 21 times and a presentation of the flags from the officers' caskets to the families of the fallen.

Owens and Richards will be buried during private funerals Wednesday. Renninger will be flown back to his home state of Pennsylvania on Wednesday for burial.