A London, Ont., homicide case could determine how far into your Facebook inbox the arm of the law could reach for investigative purposes.

The case involves Facebook messages that London police want to use as evidence in a murder investigation and trial. They've filed a production order to Facebook Canada asking for the data.

But the social media giant says it doesn't have to abide by Canadian production orders because it's an American company that stores its data in the United States.

Instead, it wants Canadian authorities to go through the so-called mutual legal assistance treaty (MLAT) process, usually used for physical evidence, which requires Canadian authorities to request that American authorities ask the FBI to compel Facebook to give up data. The American part of that process takes at least 10 months.

"There is conflicting law on this question, and it really comes down to how broadly do you read the production order power in the Criminal Code to apply to persons or companies outside of Canada who store data outside of Canada, as opposed to insisting that law enforcement go through the traditional treaty process established by the MLAT process," said Gerald Chan, a Toronto-based criminal and constitutional lawyer who focuses on digital privacy.

"This case is of huge precedential importance both for police and for tech companies like Facebook."

There have been two cases involving data stored outside of Canada used by Canadian authorities: one in Newfoundland and Labrador, and the other in British Columbia. The judges in both cases came to two different conclusions, which is partly why the London case is being watched so closely, Chan said.

'This case is of huge precedential importance both for police and for tech companies like Facebook,' a lawyer specializing in criminal and constitutional cases says. (Paul Sakuma/Associated Press)

In the British Columbia case, the Court of Appeal decided a "virtual presence" in Canada was enough to compel a company, in that case, Craigslist, to adhere to a production order.

A Newfoundland and Labrador court refused to issue a production order to a company in California because it found the order would be unenforceable outside Canada.

Criminal investigation vs. private data

With more of our lives spent online, police want to access digital data the way they would physical evidence. But tech companies are fighting back.

"Police are conducting an important investigation and they want access to relevant evidence, and so many people use platforms like Facebook and other social media platforms these days which are run by companies that are not Canadian. They store the data outside of Canada, but police don't want that to be off limits," Chan said.

"From the tech companies' perspective, it's not that they want to impede the investigation, but it's that they are, by virtue of the nature of what they do, they are servicing customers all over the world, and they have quite an understandable concern about being the subject of all sorts of court orders from all over the world just because they have a virtual presence in those jurisdictions.

"It may be one thing to get a court order from Canada, which has safeguards and a constitutional structure, but it could be an entirely different thing to get a court order from a country that doesn't have that."

Both sides are gearing up for appeals in the case as they continue to file evidence to a judge in Windsor, Ont., who is overseeing the production order dispute ahead of the court case, which will be heard in London.

For now, the homicide case is on hold as lawyers argue about the virtual evidence.