A former U.S. attorney responsible for the investigation that put "Prince of Pot" Marc Emery behind bars has joined the swelling ranks of prominent officials calling for decriminalization of marijuana.

John McKay, who spent more than five years as a federal prosecutor in Seattle, told reporters in Vancouver Wednesday that marijuana prohibition has been a "complete failure" on both sides of the border.

"I'm very pleased to be here today to discuss my support as a private citizen for the regulation and taxation of marijuana as a much better answer to the enormous threat facing citizens of both Canada and the United States because of our failed policies on marijuana," McKay said.

He spoke at a press conference organized by Stop the Violence BC, which has already gathered support for its pot decriminalization campaign from the province's chief medical officer, four former B.C. attorneys general and a growing number of municipal governments.

McKay, who is now a law professor at the University of Seattle, obtained the indictments for Emery that ended in a five-year U.S. prison term for selling marijuana seeds to Americans.

McKay said that he does not regret his prosecution of Emery.

"Mr. Emery chose to change marijuana policies by breaking them rather than advocating for change. I think that was a tremendous mistake," he said.

But McKay said that he and Emery share a fundamental belief that American and Canadian marijuana laws are seriously misguided and have become a serious threat to public safety.

"We are, through our policies, promoting a huge black market with billions of dollars that are being exploited through criminal cartels, through gangs, though organized crime on both sides of the border," McKay said.

He pointed to the scores of Canadians sentenced to jail time in the U.S. in recent years for arranging deals with Mexican cartels to provide B.C.-grown pot in exchange for guns or cocaine and methamphetamines.

"This is an enormously potent and dangerous environment, which it is only fair to say, is created and maintained by our failed criminal marijuana prohibition," McKay said.

The lawyer is a sponsor of Initiative 502, a pot legalization proposal that will appear on Washington State ballots in November. If approved, the initiative would make it legal for adults to possess up to one ounce of marijuana, while sales to minors and driving under the influence would be forbidden.

McKay said that 75 years of marijuana prohibition have failed to convince North Americans that it's wrong to smoke pot, and the threat of jail has done nothing to dissuade users. Every year, about 10,000 people in Washington State and close to 1 million across the U.S. are imprisoned for simple possession of marijuana.

"I think it's really important that when societies choose to criminalize behaviour, we have broad agreement and support that that behaviour is criminal," he said.

"I don't think there is broad agreement that persons with guns and badges, judges with authority, jailors with jails and prisons, should be used for this."

McKay added that he does not believe legalizing marijuana in Canada would result in a backlash from American officials, explaining that a very similar debate is now happening south of the border.

Emery's wife Jodie also spoke at Wednesday's press conference, and said it was a "wonderful thing" to see respected legal professionals like McKay support marijuana legalization.

But despite the efforts of groups like Stop the Violence, Prime Minister Stephen Harper has repeatedly stated that the issue is not up for debate. At the Summit of the Americas in Colombia this weekend, the Canadian leader acknowledged that the war on drugs is not working, but joined the American contingent in rebuffing Latin American leaders' push for decriminalization.