How did a killing at a Sikh temple lead to Canada and India expelling each other's diplomats?

Relations between India and Canada are at a low point as the countries expelled each other’s top diplomats over an ongoing dispute about the killing of a Sikh activist in Canada. Canada said it had identified India’s top diplomat in the country as a person of interest in an assassination plot and expelled him and five other diplomats Monday. India has rejected the accusations as absurd, and its foreign ministry said it was expelling Canada’s acting high commissioner and five other diplomats in response. It’s the latest in an escalating dispute over the June 2023 killing of Sikh activist Hardeep Singh Nijjar.