Its legitimacy dented and testimony roster depleted, the beleaguered Missing Women Commission of Inquiry begins its hearings today to find out why serial killer Robert Pickton was able to continue his Downtown Eastside murder spree while already a police suspect.

The hearing is beginning under a cloud of controversy after the withdrawal of 20 of the 21 groups given standing by the head of the commission, former attorney general Wally Oppal.

Many organizations are furious the province will pay for lawyers to represent testifying police officers and family members of Pickton's victims, but not aboriginal, sex worker and women's groups.

On Thursday, Amnesty International and the B.C. Civil Liberties Association announced their withdrawal.

A slew of DTES women, mostly sex workers, went missing throughout the late 1990s and early 2000s.

Pickton was already a prime police suspect even as women continued to vanish.

According to a VPD report, completed in 2005, Vancouver police knew as early as August 1998 that the Port Coquitlam pig farmer "was the likely killer and all information was passed on to the Coquitlam RCMP."

Pickton was arrested three years later. He was eventually sentenced in 2007 for the second-degree murders of six women; another 20 charges were eventually stayed.

The remains of 33 women were found on his farm. In 2002, however, he complained to a jailhouse informant that he'd fallen just short of his goal of killing 50 women.

The inquiry begins at 10 a.m. at the Federal Courthouse on W. Georgia St.

A Downtown Eastside coalition created between the Downtown Eastside Women's Centre and the Women's Memorial March Committee - which had also dropped out - plans to rally, calling for a new fair and inclusive inquiry.