Canadian police have arrested three Indian nationals over assassination of Sikh separatist leader Hardeep Singh Nijjar last year, which sparked a diplomatic tension between Ottawa and New Delhi.

The Canadian police made the first arrests regarding the murder on Friday in Edmonton, Alberta, charging the accused named as Karanpreet Singh, 28, Kamalpreet Singh, 22 and Karan Brar, 22, with first-degree murder and conspiracy to commit murder.

Diplomatic ties between two former British colonies hit rock bottom after Canadian Prime Minister Justin Trudeau accused the “agents of the government of India” of planning the shooting.

Mandeep Mooker, the Royal Canadian Mounted Police (RCMP) superintendent and head of the Integrated Homicide Investigation Team for the Mounties, told a televised news conference that they were interrogating whether the three culprits have ties, if any, with the Indian government.

“This investigation does not end here,” Mooker said. “We are aware that others may have played a role in this homicide, and we remain dedicated to finding and arresting each one of these individuals.”

Nijjar, a Canadian citizen, leader of the Khalistan Tiger Force (KTF) who advocated for the establishment of Khalistan, a separate Sikh homeland, was fatally shot while sitting in his vehicle outside a Sikh temple in Surrey, British Columbia on the evening of June 18th.

The assailants, two masked men, fled the scene by running through a park and disappearing.

In India, Nijjar was a wanted terrorist, with a reward of one million Indian rupees offered for his capture.

The Khalistan movement aims to establish an independent Sikh state in the Punjab region of India and Pakistan, advocating for Sikh separatism.

The existence of Sikh separatist organizations in Canada, which houses the world’s largest Sikh diaspora community, along with the US and the UK has been a source of ongoing frustration for the Indian government.

Three months after the murder, Trudeau declared in the House of Commons that Canada was looking into “credible allegations” that could potentially connect the Indian government to the assassination.

The Indian government has dismissed the accusations as “absurd” and urged the Canadian authorities to crack down on the activities of individuals it calls “terrorists”, a reference to Sikh separatists.

The diplomatic row worsened after Canada expelled the head of India’s intelligence agency Research and Analysis Wing (RAW), in Canada, Pavan Kumar Rai, who was accused of either ordering or assigning someone to kill Nijjar.

India also expelled a Canadian diplomat, and further suspended visa applications for Canadians.

The tussle forced Ottawa to withdraw two-thirds of its diplomats based in India.

In November last year, American authorities revealed that an Indian government official was implicated in a conspiracy to carry out the assassination of Gurpatwant Singh Pannun, another Sikh separatist who holds dual citizenship in the US and Canada.