VANCOUVER - Families of serial killer Robert Pickton victims have known the answer to who killed their loved ones for years.

On Tuesday, the process aimed at understanding why he was able to do it, how he was able to conduct such a prolific killing spree for so long, will get underway.

The families have been calling for public hearings since before Pickton was arrested and eventually convicted of six murders. For them, the convictions represent a frustratingly small number of victims and belies the scale of his crimes and the failings of the police and justice system to stop him.

Pickton's trial brought out the gruesome details of the killings themselves, but it only revealed what happened, not why.

Those answers are more complicated, and so too is the task of the Missing Women Commission of Inquiry, ordered by the B.C. government last year after Pickton's final appeals were exhausted.

"The trial of Pickton just focused on his culpability, and not the quality of the police investigation. It didn't address why it took so long to apprehend that murderer," said lawyer Cameron Ward, who is representing the families of at least 17 of Pickton's victims at the hearings.

"I think our society has the right and the need to determine why the investigation unfolded the way it did, and why, for so many years this man was allowed to prey on vulnerable women in the Downtown Eastside."

Pickton was arrested in 2002 and convicted of six counts of second-degree murder. The remains or DNA of a total of 33 women were found on his farm, and he bragged to police that he killed 49.

He lost his final appeal at the Supreme Court of Canada last summer, clearing the way for the public inquiry.

The public inquiry will examine the role of the Vancouver police and the RCMP, and why neither force was able to stop a serial killer -- or even acknowledge that one existed -- as sex workers vanished in the late 1990s and early 2000s.

There have been persistent allegations the police did not take those reports of missing women seriously, didn't trust the sex workers, or simply didn't care.

The hearings will also look at the role of Crown prosecutors who, in 1998, decided not to charge Pickton with attempted murder after a sex worker was brutally assaulted at his farm a year earlier. Pickton remained free, and many of his victims were killed in the years that followed.

Some of the lawyers in the downtown Vancouver courtroom will almost certainly turn the focus on what advocates say are systemic problems that force impoverished, drug-addicted women into the dangerous sex trade in the first place.

Those issues aren't specifically in the inquiry's terms of reference. However, a set of less-formal hearings known as a "study commission" has already touched on some of them.

There will be allegations of negligence and wrongdoing, and lawyers for the families, the police, the government and others will argue about what changes are needed to prevent more vulnerable women from disappearing and dying.

"I'm not confident that sufficient lessons have been learned," said Ward.

"This was Canada's most horrific mass serial murder, and nothing I've read so far has convinced me that something similar couldn't happen again."

The hearings will also be the subject of continued controversy over legal funding for non-profit advocacy groups that were granted participant standing by commissioner Wally Oppal but were denied legal funding from the provincial government.

Nearly all of the groups that Oppal recommended receive funding have withdrawn, saying they simply can't afford to pay for a lawyer to cross-examine witnesses and present counter arguments to the well-paid legal teams of the provincial government and police.

Several of those groups plan to stage a rally Tuesday morning outside the Federal Court building where the inquiry will be held.

Critics say the government's refusal has shut out the voices of the same vulnerable groups that were victimized by Pickton a decade ago, who weren't listened to then and won't be listened to now.

"It's heartbreaking -- it's exactly what went wrong in the first place, what's going on right now," said Kate Gibson of the WISH drop-in centre for sex workers, one of the groups that was granted status but denied funding.

"If we don't have counsel to participate and others don't have counsel to participate, it's as if the lawyers are talking to one another. When you don't have a full complement of voices, I'm not quite sure what that final report could look like."

Two independent lawyers have been appointed to broadly represent the interests of Downtown Eastside residents and aboriginals, and have been inviting input from the unfunded groups. Some of those groups have vowed to boycott the independent lawyers, while others are prepared to work with them.

The provincial government maintains it can't afford to provide more legal funding.

"We believe that there is adequate legal counsel for the families that have been impacted, and we expect the commission to continue," said Attorney General Shirley Bond.

Bond suggested public inquiries are different from trials and participants don't need lawyers. The province's Criminal Justice Branch is paying high-profile lawyer Len Doust to represent its interests at the hearings.

With or without the input of those advocacy groups, the inquiry will continue, hearing from dozens of witnesses in the coming months including academics, police officers and sex workers. It's not clear how long that will take.

In the end, Oppal will provide a report explaining why the system failed Pickton's victims and what should be changed.

Commission lawyer Art Vertlieb said he believes the inquiry will fulfil that mandate.

"I'm fully confident that with many good lawyers and the participants that were involved that we will sort out what happened and make recommendations that will be helpful," said Vertlieb.

"If we're not going to make a difference going forward, then why are we doing this? We're doing this because we think the issues are important and we want to make a difference."