Canadian police announced Friday that they had arrested three people involved in the murder of a Sikh separatist leader last June in the suburbs of Vancouver, triggering a diplomatic conflict with India.

Royal Canadian Mounted Police Deputy Commissioner David Teboul said three suspects were arrested and charged with the murder of Hardeep Singh Nijjar, 45, by masked gunmen in Surrey, near Vancouver. However, he said police could not comment on the nature of the evidence or the motive. “This matter is under active investigation,” Teboul said.

Canadian Prime Minister Justin Trudeau sparked a diplomatic row with India in September when he said there were “credible allegations” of India's involvement in Nijjar's killing. India had accused Nijjar of having links to terrorism, but strongly denied any involvement in the killing.

Nijjar, a Canadian citizen born in India, was a plumber and leader of what remains of the once-powerful movement to create an independent Sikh homeland, known as Khalistan. But he has denied accusations of links to terrorism.

The three suspects are Kamalpreet Singh, Karan Brar and Karampreet Singh and were arrested in Edmonton, Alberta, said Mandeep Mooker, superintendent of the Royal Canadian Mounted Police.

“This investigation does not stop there. “We know that other individuals may have played a role in this homicide and we remain committed to finding and arresting each of these individuals,” Mooker said.

A bloody Sikh insurgency rocked northern India in the 1970s and 1980s until it was crushed by a government offensive, in which thousands were killed, including prominent Sikh leaders .

The Khalistan movement has lost much of its political power, but it still has supporters in the Indian state of Punjab, as well as among the large Sikh diaspora in the rest of the world. While the active insurgency ended years ago, the Indian government repeatedly warned that Sikh separatists had attempted to return.