Robert Pickton's victims from top left: Sereena Abotsway, Mona Wilson, Angela Joesbury, Brenda Wolfe, Georgina Papin and Marnie Frey. (CBC)

Robert William Pickton will not get a new trial for the murder of six women in British Columbia, the Supreme Court ruled Friday.

The unanimous ruling all but guarantees that the former B.C. pig farmer will not face further legal action in a string of deaths that horrified the country, provincial justice officials told a news conference shortly after the ruling.

He was also charged in the deaths of 20 other women, mostly troubled residents of Vancouver's Downtown Eastside, but that prosecution will likely be discontinued to spare families and the court system from the effort and expense of another long trial.

"In reaching this position, the branch has taken into account the fact that any additional convictions could not result in any increase to the sentence that Mr. Pickton has already received," B.C. Crown spokesman Neil MacKenzie told a press conference Friday in Vancouver after the ruling.

In December 2007, Pickton was found guilty of six counts of second-degree murder in the deaths of Sereena Abotsway, Mona Wilson, Andrea Joesbury, Georgina Papin, Marnie Frey and Brenda Wolfe. He was sentenced to life in prison with no chance of parole for at least 25 years, which is the maximum sentence under Canadian Law for murder.

Deputy Chief Const. Doug Lepard of the Vancouver Police Department apologized on Friday for mistakes made by the force. (CBC)

Deputy Chief Const. Doug LePard of the Vancouver police issued an emotional apology "from the bottom of my heart" to the victims' families at the press conference Friday.

"I wish that all the mistakes that were made we could undo and I wish more lives would have been saved. So on my behalf and [on] behalf of the Vancouver police department ... I would say to the families how sorry we all are for your losses and because we did not catch the monster sooner."

No 'legal error': top court

Although criminal convictions will likely not be pursued in the other 20 cases, the task force looking into them as well as other such cases, will remain active, said RCMP assistant commissioner Al MacIntyre.

"There's still 39 outstanding cases of missing women that are being fully examined and pursued. The joint task force remains committed to our promise to continue to investigate the cases of these missing women until we have exhausted all possible avenues.…You have my word on that."

At a separate press conference Friday in Vancouver, B.C. Attorney General Michael de Jong acknowledged that victims' families were left with many unanswered questions, and said a decision on whether to hold an inquiry will be made soon.

"To the extent that an inquiry can fill in those blanks, it's another argument to hold one," said de Jong. "I'm not ruling an inquiry out, but I'm not in a position to tell you one is being called today."

Canada's top court has upheld the conviction of Robert Pickton, who was sentenced to life in prison with no chance of parole for at least 25 years in the deaths of six women. (Canadian Press)

Pickton's lawyers had filed an appeal to the top court based on instructions that B.C. Supreme Court Justice James Williams gave to the jurors, which Pickton's defence claimed had robbed him of a fair trial.

Before delivering their verdict, the jurors had asked the judge whether they could convict Pickton without being certain he was the only person involved in killing the six women. Williams said it was sufficient to find Pickton was an active participant.

When the appeal was launched, the Crown countered that even if there was a mistake, it wasn't serious enough to warrant a new trial.

In its ruling Friday upholding the conviction, the top court said there was "overwhelming evidence" against Pickton and "no miscarriage of justice was occasioned in this trial."

Justice Louise Charron wrote: "This case was never about whether the accused had a minor role in the killing of the victims. It was about whether or not he had actually killed them.

"Having regard to the overwhelming evidence about the accused’s having been actively involved in the actual killing of the victims, either by acting alone or in concert with others ... there was neither a legal error ... nor a miscarriage of justice."

Family says ruling gives closure

The sister of one of Pickton's victim's, Georgina Papin, told CBC News Friday from Edmonton that the family was happy and relieved with the ruling because it allows them to put some closure on her death.

Cynthia Cardinal, the sister of victim Georgina Papin, says her family is happy with the top court's decision. (CBC)

"These last few years have been really ... an emotional roller-coaster," said Cynthia Cardinal. "It just felt like he [Pickton] has more rights than the victims and the families. It just felt like he was getting everything that he wanted and we were just left, like, helpless."

Now her sister can finally rest in peace, Cardinal said. "I can feel her around me every day. I know that today's probably a good day for her."

At least two family members of Pickton's suspected victims are calling for a public inquiry into the case.

"I'm ready and prepared to live with the outcome of today's decision at the Supreme Court," said Ernie Crey, whose sister Dawn Crey's DNA was found on Pickton's farm. "This man is in jail. He's not going to harm anyone else. His feet won't touch the pavement any time in the future.

"But for me, that chapter is now closed. I'm going to turn my attention to the government of British Columbia and the public outcry for a public inquiry."

'There needs to be an inquiry into why they [police] didn't do more right from the beginning when they found out that women were going missing and when they heard about that farm.'—Sandra Gagnon

Sandra Gagnon's sister, Janet Henry, went missing in 1997. Henry used to party at Pickton's home. Gagnon said the missing women's task force is almost certain she died there. Now, she fears they'll never know.

"There needs to be an inquiry into why they [police] didn't do more right from the beginning when they found out that women were going missing and when they heard about that farm," Gagnon said.

The fact that murder charges in the slayings of 20 other women may be stayed does not sit well with some of the other victims' families.

"There's families that their daughters have gone missing and they know darn well he had them on the farm ... They're going to their grave never knowing what happened and never having accountability for their loved ones," said Lynn Frey.

Pickton was convicted of her sister Marnie Frey's murder in 2007.