Image copyright Getty Images Image caption Prosecutors claimed Robert Pickton confessed to 49 killings

A memoir apparently written by a Canadian serial killer has been withdrawn within hours of appearing for sale online.

Former multi-millionaire pig farmer Robert Pickton was convicted in 2007 of murdering six women. Charges relating to 20 other deaths were suspended.

Another inmate helped him smuggle the book out of prison, CTV reported.

The publisher requested its removal from retailer Amazon and apologised to victims' families.

In a statement, Colorado-based Outskirts Press, which specialises in helping authors self-publish their work, said it had a "longstanding policy of not working with, nor publishing work by, incarcerated individuals".

"Mr Pickton was apparently aware of our no-tolerance policy when he devised a plan to publish through an unaffiliated third party," the company said. The third party, named by the company as Mr Chilldres, told them he was the sole owner and author of the book.

Robert Pickton case

Image copyright Getty Images Image caption A memorial was left at Pickton's pig farm for the women who went missing

The first woman disappeared from Vancouver's deprived Eastside district in 1983, with a spike in the numbers going missing in 1995

The police were accused of being slow to act, partly because many of the women were drug addicts or sex workers

Police searched Pickton's farm in 2002, finding some of the missing women's possessions and remains

One of the most expensive trials in Canadian history opens in 2007, with the judge comparing the case to a horror film

Pickton convicted on six counts of murder

Vancouver's dirty little secret

City's vanished women

Officials in British Columbia had earlier vowed to prevent Pickton from profiting from sales of the memoir, entitled Pickton: In His Own Words.

"It is not right that a person who caused so much harm and hurt so many people could profit from his behaviour," said the province's Minister for Public Safety, Mike Morris, in a statement.

British Columbian officials also asked Amazon to stop selling the memoir, while Amazon users had also called for it to be removed and gave it the lowest possible rating. The company has not yet commented on the book's appearance on its site.

'Deeply troubled'

Canadian Public Safety Minister Ralph Goodale said an investigation had been launched into how Pickton's manuscript was smuggled out of the maximum security Kent Institution prison where he is being held.

But CTV reported that Pickton bypassed checks on his own correspondence by passing the book to a fellow inmate, who sent it to a friend in California, Michael Childres.

In the book, the serial killer said he was innocent and was framed for the killings by Canadian police, the Vancouver Sun reported.

Ernie Crey, whose sister Dawn's DNA was among that of 33 women found at Pickton's Port Coquitlam pig farm, said he was "deeply troubled" by the book.

Lori Shenher, who helped bring Pickton to justice and wrote her own book on the case, wrote that she hoped people would ignore it "in the interest of common decency".

Pickton was sentenced to life in prison with no chance of parole for 25 years after initially being charged with the murders of 26 women from a total of 69 who had gone missing.

He killed the women at his farm and fed some of their remains to his pigs.

During the trial, prosecutors claimed Pickton had confessed to 49 killings to an undercover police officer posing as a cellmate.