Police investigating the case of Vancouver's missing women did not have a prime suspect until Robert William Pickton's arrest in February 2002, jurors in his trial heard Thursday.

RCMP Sgt. Margaret Kingsbury told B.C. Supreme Court in New Westminster that police were still reviewing files on nearly 500 attacks on sex trade workers in the hunt for a serial killer — or killers.

"The theory was that this person or persons may have entered the police universe at one point in time and potentially wasn't successful all the time in killing women," Kingsbury testified. "Potentially there would be some unsolved crimes out there."

In the pocket of a jacket at the foot of Pickton's bed, Kingsbury found a piece of paper with an address and the name Andrea on it, she said. The address is the last known address of Andrea Joesbury, one of the women Pickton is accused of killing.

In his office, among piles and boxes of clothes, officers found a syringe filled with blue liquid on a television stand.

Green River killer once person of interest

Earlier Thursday, Kingsbury told the court that anyone with a history of violence against sex-trade workers was a suspect, including the Green River killer in the U.S., who was one of at least 500 people of interest.

Gary Ridgeway later pleaded guilty in 2003 to the murders of 48 women in Washington State. The murders of women in the Seattle area, most of them runaways and prostitutes, began in 1982. 

Kingsbury said the Seattle task force probing the Green River slayings told Canadian authorities to hit the streets and talk to prostitutes about "bad dates" — men who were violent clients or refused to pay.

Pickton is being tried on six of 26 charges of first-degree murder in the deaths of missing women from Vancouver's Downtown Eastside, with a second trial to be held later. He has pleaded not guilty to all charges.

'Bad date' queries began in 2001

The Vancouver investigation into dozens of women who had been reported missing from the Downtown Eastside began in 2000 and involved a number of police agencies, Kingsbury testified.

But it wasn't until the middle of 2001 that police decided to take a proactive approach to their investigation. By that time, it was apparent there were 45 women missing — double the number investigators originally had thought.

"What that was was a body of people who would go down to the Downtown Eastside and speak to sex-trade workers and determine who was a good date, who was a bad date," Kingsbury said.

Sandra Gagnon said that was too late to find her sister, Janet Henry, who disappeared 10 years ago.

"It is frustrating because I know if it was women from any other part of town … not drug addicts or hookers, that more would have been done," Gagnon told CBC News Thursday.

Daphnie Pierre has been told the DNA of her sister, Jackie Murdoch, was found on Pickton's farm, but no one has been charged in her disappearance.

"I think that it is disgusting that it took them so long to find out something," Pierre said. 

"Took them two years to get on this farm, to find out anything. And then all of a sudden they started talking about it on the news and the media, then they [police] started doing something."

Massive database detailed

Kingsbury also gave details of her work as a field investigator involved with the RCMP's massive database devoted to the case, which contained more than 3,000 crime files of murders, attempted murders or sex assaults of sex-trade workers and hitchhikers provincewide.

The objective of the database was to locate crime-scene DNA and identify possible suspects, she said.

"We looked at what Vancouver city police had done to attempt to find these 27 missing women over a period of time and the checks they made," she said.

"We assumed that these women weren't missing any longer, but they were deceased. But we did keep an open mind."