The Vancouver police and the RCMP have both faced allegations that missteps by individual officers and apathy among senior management led to badly flawed investigations that were unable to stop Pickton, even as it became more likely that he was behind the disappearances of sex workers from the Downtown Eastside.
Both have offered apologies for not doing more, but neither will accept blame. The Vancouver police insist that the fault lies at the feet of the RCMP, while the Mounties argue the opposite.
The two forces were conducting separate but related investigations in the late 1990s and early 2000s: Vancouver into the disappearances of sex workers, and the RCMP into Pickton as a potential suspect.
Eventually, the police combined forces to form a joint investigation, dubbed Project Evenhanded, which was formed to look for links between missing sex workers.
Vancouver police lawyer Tim Dickson told the inquiry that while police in the city investigated missing person cases involving sex workers, the Mounties took responsibility for the investigation of Pickton because he lived in their jurisdiction.
The RCMP appeared to take the investigation seriously at first, said Dickson, vigorously investigating tips implicating Pickton in 1998 and 1999.
But by late 1999, the investigation appeared to grow stale. The lead RCMP investigator was transferred off the case and months at a time passed during which nothing was done on the file, said Dickson.
"The real failure of the Pickton investigation is that chronicle of inaction," said Dickson.
"The great shame of this is that this was the police force's best chance to stop the killings by catching the killer. Coquitlam RCMP's failure to pursue the Pickton investigation with the vigour and the resources it required is really the heart of the police force's failings in relation to the tragedy of the missing women."
While the Vancouver Police Department has acknowledged its own senior officers were slow to realize a serial killer was operating in their city, Dickson said the department's greatest fault was not pressing the RCMP to do more to investigate Pickton.
The RCMP, however, rejected the Vancouver Police Department's suggestion that the Mounties were solely responsible.
RCMP lawyer Cheryl Tobias said the two forces should have combined their efforts much earlier, but she said that didn't happen because Vancouver police were slow to realize the gravity of the investigation.
"There was a delay in forming a formal joint-forces operation of the kind that was necessary to deal with the complex and extensive investigation," she said.
"But the evidence has shown that the delay was mostly, if not entirely, due to the delay that occurred in the management in the Vancouver Police Department coming to realize that a serial offender likely was involved."
In addition, Tobias said one of the reasons the RCMP's investigation slowed in 1999 and 2000 was because Vancouver police did not tell RCMP investigators that women were still disappearing. That mistaken belief meant the RCMP didn't consider the case to be an urgent public safety concern, she said.
Tobias said officers on the ground did the best they could with the information they had at the time, but she said all they had was a series of uncorroborated tips, which didn't amount to proof that Pickton was the only suspect worth pursuing.
"Hindsight is the wrong lens to use to evaluate past conduct," said Tobias.
"It should not be used to judge the efforts of those who did not have the advantage to know how things ultimately turned out."
Both forces have issued apologies for not doing enough to catch Pickton — the Vancouver police in 2010, and the RCMP earlier this year. But both forces have also insisted their officers did the best they could at the time and they shouldn't be judged with the benefit of hindsight.
Commissioner Wally Oppal has heard from dozens of witnesses, including current and former members of the Vancouver police and the RCMP.
His final report, due by Oct. 31, will detail what each police force did and resolve conflicts in the testimony at the inquiry. While he can't assign legal blame or liability, Oppal can make findings about whether either force or their officers acted properly or ought to have done more.
Closing arguments are scheduled to wrap up on Wednesday.
Pickton was arrested in February 2002 and eventually convicted of six counts of second-degree murder.
The remains or DNA of 33 women were found on his farm, though he told an undercover police officer that he killed a total of 49.