The only reasonable explanation for the disappearance of dozens of sex workers from Vancouver's Downtown Eastside in the late 1990s was that they were being murdered by a serial killer, the public inquiry into the Robert Pickton case heard Tuesday.

And the Vancouver Police Department's "embarrassing" failure to recognize that reality was one of the key reasons Pickton wasn't caught sooner, said former detective Kim Rossmo, who has been credited as being the first to warn that a serial killer was on the loose only to be ignored by his bosses.

Rossmo was a PhD-educated geographical profiler with the Vancouver department when, in late 1998, he was brought into the investigation of missing sex workers from the Downtown Eastside.

By the following spring, Rossmo prepared a report that offered a statistical analysis of missing persons reports from the troubled community.

He found a sudden and unmistakable spike beginning in 1995, which continued to rise dramatically in 1997 and 1998.

That increase was too large to be a coincidence, Rossmo concluded, and the fact that the women remained missing for so long -- when most missing people surface after just a couple of weeks -- suggested they had met foul play.

Finally, the lack of any bodies, which is highly unusual in murder cases, and the fact that all of the women were sex workers suggested they were victims of the same killer, he said.

"I thought that the data could only be adequately explained by the possibility of a serial killer," Rossmo told the inquiry.

"The only thing that I thought made sense that we had a single serial murderer or maybe two people working together causing these disappearances."

But Rossmo ran into resistance from other investigators and his superiors, who had their own theories about what happened to the women.

Those other theories included that the women hadn't disappeared at all, but simply moved to another city to ply their trade. Others suggested the women were the victims of drug overdoses or drug violence, or that their pimps were killing them.

"It is a little bit embarrassing for me to tell you that my former department was putting forth some of these Hollywood-style theories," said Rossmo.

"The typical Vancouver pimp was a boyfriend, not somebody driving around in a Cadillac with a fancy hat. And what would be the point of killing two dozen working women? There is pimp violence, but this makes no sense."

Rossmo said the failure to recognize that possibility for at least another year was the main reason the Vancouver police failed to crack the case of the missing women.

If the force took his warnings seriously, said Rossmo, the investigation would have been given the attention and resources it deserved much earlier.

"The main thing that the Vancouver department got wrong is the refusal to accept the serial killer, at least in any timely fashion," said Rossmo.

"If management really felt there was a legitimate risk of a serial killer, I'm sure they may have fought much harder for more resources."

That resistance extended to the head of the force's major crime unit, Insp. Fred Biddlecombe, who was in charge of murders, sex crimes and missing persons.

Rossmo testified that Biddlecombe rejected the serial killer theory from the very beginning, insisting the women weren't missing at all and would be found eventually.

In the fall of 1998, Rossmo joined a working group that was brainstorming ways to investigate reports of missing sex workers.

The group was about to issue a news release announcing that the force was looking into whether a serial killer was targeting the women when Biddlecombe intervened, blocking the release and disbanding the team.

"One of the common mistakes repeated over and over again by police agencies with serial murder investigations is the initial denial that there is a serial murderer, which inevitably ends up in resulting in a lot of negatives, both with the community and the media," Rossmo testified.

"There is a duty to warn the public regarding potential threats. It's not our right to not warn people."

Instead, the Vancouver police continued to insist publicly that there was no evidence to suggest a serial killer was behind the disappearances.

That continued until November 1999, when spokeswoman Const. Anne Drennan acknowledged for the first time that one or more serial killers could be at work.

The inquiry has also heard allegations that a personality conflict between Rossmo and Biddlecombe contributed to Biddlecombe's failure to take the missing women investigation more seriously.

Rossmo testified that Biddlecombe was immediately hostile, and described a "tantrum" during a meeting with the working group in late September 1998. Rossmo said Biddlecombe accused him and another officer of leaking information to the media, and said the serial killer theory was simply wrong.

"I found him to be arrogant and somewhat egotistical," said Rossmo. "It was clear that he didn't want to deal with this issue, didn't like what we were doing, didn't want to work with us."

It was the second -- and final -- time the working group met.

"In effect, given his position, which was the officer in charge of homicide, sex crimes and missing persons, he basically killed the working group," said Rossmo

"There was no way we would continue without his full co-operation."

Rossmo left the Vancouver police in acrimony in December 2000.

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.

Rather than accept a lesser-paying job as constable, Rossmo left. He sued the force for wrongful dismissal, but lost after a sensational trial and a subsequent appeal.

He now teaches at Texas State University.

Pickton wasn't caught until February 2002, prompting a massive search of his farm that uncovered the belongings and remains of 33 women.

He was convicted of six counts of second-degree murder, but he claimed to have killed 49.