Former detective Kim Rossmo, who was a geographic profiler with the force, said Pickton wasn't caught sooner because senior police management resisted the theory that the women were being murdered by a serial killer.
"I think there was a good chance it could have been solved by the end of 1999 if the appropriate resources were deployed and the Vancouver police department was properly engaged in this and had accepted the serial killer theory," Rossmo told the inquiry, stressing it was a rough estimate.
"I don't want to give overemphasis to my estimate of the end of '99, but it certainly should have been solved much sooner. ... I believe my evidence from the other day was I think this case could have been solved one to two years earlier than it was."
Pickton wasn't arrested until February 2002, when an RCMP officer in nearby Port Coquitlam obtained an unrelated warrant to search Pickton's farm for illegal firearms.
Between late 1999 and his arrest, a dozen more women who were later connected to Pickton's farm disappeared.
Rossmo was among the first officers to suggest in 1998 that a rash of missing person reports involving Downtown Eastside sex workers could be related to a serial killer.
The following spring, he produced a statistical analysis that concluded the women were almost certainly the victims of a single killer.
But he said he faced immediate resistance, namely from Insp. Fred Biddlecombe, who was in charge of the force's major crime unit. Rossmo testified that Biddlecombe didn't believe the women were killed and instead thought they would surface on their own given enough time.
Rossmo said that meant the force didn't take the case seriously and didn't devote the resources needed for a complicated serial murder investigation.
Rossmo said Biddlecombe appeared to honestly believe there was no serial killer, and he stressed his complaint isn't that the inspector was wrong.
Rather, Rossmo said there were no options to challenge Biddlecombe's opinion, partly because Biddlecombe himself was antagonistic and partly because of the force's strict adherence to the chain-of-command, which made it impossible to go above Biddlecombe's head.
Rossmo said there needs to be a system that allows debate to ensure a single, high-ranking officer can't act as the final word on how investigations proceed.
"It would have to be formalized and thought would have to be given to how to prevent groupthink and to prevent the command structure from dominating," said Rossmo.
"The investigative opinions should be based on evidence, information, knowledge and experience, not just by the number of stars and stripes on someone's uniform."
Another factor, Rossmo said, was the identity of the victims.
Rossmo said the fact the women were poor, drug-addicted sex workers from the Downtown Eastside meant the public and the media weren't putting pressure on the force, which allowed police management to remain apathetic.
"Your opinion is that if the women who went missing and were subsequently determined to be murdered by Willie Pickton had been from Vancouver's west side, the case would have been handled differently?" asked Cameron Ward, a lawyer representing the families of 25 missing and murdered women.
"Yes," replied Rossmo.
The force eventually did adopt the serial killer theory, but Rossmo said it was far too late.
Rossmo and other officers were considering the possibility of a serial killer as early as September 1998, and by then investigators were already receiving tips implicating Pickton.
But as far as the public was concerned, there was no serial killer.
The force's main spokesperson at the time, Const. Anne Drennan, continued to insist the serial killer theory was a red herring, telling a reporter in April 1999: "There is absolutely nothing that has come to light that indicates that there is ... a serial killer on the loose, as some activists suggest."
Rossmo said Drennan's statement was wrong.
"This statement is not accurate, it's not true," said Rossmo. "Given what we knew by April, maybe even by February, we definitely did have reason to be fearful of this being the case."
An internal Vancouver police report concludes Drennan was making such statements under the direction of Biddlecombe. Drennan didn't acknowledge the possibility of a serial killer until November 1999.
Rossmo is expected to face tough cross-examination from lawyers for a number of police officers, including Biddlecombe.
Rossmo left the Vancouver police in December 2000, setting off an ugly wrongful dismissal lawsuit that Rossmo eventually lost.
He had been given the title of detective inspector for a five-year contract to run a geographical profiler unit, but the force decided to discontinue the project.
He was offered a lesser-paying job as constable, but Rossmo rejected the offer and left. A judge later concluded the Vancouver police didn't have an obligation to keep Rossmo at the rank and pay of inspector once his contract had ended.
He now teaches at Texas State University.
Pickton is now serving a life sentence with no change of parole for 25 years after he was convicted of six counts of second-degree murder.
The remains or DNA of 33 women were found on his farm. After his arrest, he told an undercover police officer that he killed 49 women.