What are the 'Five Eyes'? As Canada accuses India, what you need to know about the intelligence alliance

Following Canada's accusation this week that agents with connections to the Indian government were responsible for the fatal shooting on Canadian soil of Hardeep Singh Nijjar, Canada's Five Eyes allies have so far been reluctant to wade too deeply into the incident. 

The CBC's Evan Dyer reported this week that Canada had already indicated to the U.S. and the U.K. during and immediately following the G20 summit in New Delhi earlier this month that Canada's already difficult relations with India were about to get even rockier. 

The public accusation has put Canada's top allies in an uncomfortable position while the West tries to pull India into a closer relationship as a potential ally against China, with the U.S. even creating the so-called "quad" alliance between the U.S., India, Australia and Japan. 

Intelligence and national security expert Wesley Wark says all of the partners — including Canada — are in the same boat.

"They all have a really significant interest in trying to maintain good relations with India, to try and advance economic ties, to try and advance military ties in the context of looking for ways to counter China's expansion in the Asia-Pacific arena," he said. 

The U.S., however, denied it refused to support Canada after a Washington Post report said Ottawa had tried and failed to get its four top allies — known collectively with Canada as the Five Eyes — to publicly condemn the murder.

A senior U.S. administration official told CBC News, "In fact, we very clearly and very publicly have done the opposite by expressing deep concern shortly after PM Trudeau made the announcement."

Here's a brief reminder of what Canada's intelligence alliance is — and why it's especially important to Canada right now.

The Five Eyes is an intelligence sharing network made up of the U.S., the U.K., Canada, Australia and New Zealand. 

Its roots date back to an alliance originally created in 1946 between the United States and the United Kingdom as a way to share intelligence signals. 

It was expanded in 1948 to include Canada and in 1955 to include Australia and New Zealand. 

Other countries, termed "third party partners," share information with the alliance but are not formal partners.  

The Five Eyes pool resources and share intelligence with each other. As technology has changed through the decades, the way countries gather and share information has, too. Where once they may have relied on radio signals, today much of it is done through digital tracking and interception. 

Not every country contributes equally.