Ties between India and Canada are at their lowest point in years after the assassination of a Sikh separatist leader in Canada. Hardeep Singh Nijjar, an Indian-born Canadian, was shot and killed in the parking lot of a Sikh temple in British Columbia in June this year. Now, Canada’s prime minister, Justin Trudeau, has said that there are “credible reasons” to believe that Indian government agents were involved. India has dismissed these allegations as "absurd and motivated” and has now suspended all visas for Canadian citizensEach country has also expelled one senior diplomat.But what lies behind the escalating tensions?