Authorities on Tuesday announced charges against the leader of an Indian criminal group in connection with the political assassination of a prominent Sikh leader in Canada, a high-profile killing that strained the diplomatic relationship between Canada and India at the time.

The charges were part of a massive law enforcement operation involving agencies across the United States, Canada and Europe that arrested 37 defendants allegedly part of three Indian international criminal syndicates linked to kidnappings, extortion, racketeering, firearms trafficking, drug trafficking and murder, U.S. Attorney Bill Essayli announced at a news conference Tuesday. He spoke alongside officials from the Los Angeles Police Department, the FBI and the Royal Canadian Mounted Police. Authorities are still searching for seven fugitives in the United States, two in India and one in Europe.

The groups “have fueled violence, fear and instability within East Indian communities throughout California and abroad,” said Patrick Grandy, assistant director in charge of the FBI’s Los Angeles field office.

Lawrence Bishnoi, 33, and his childhood friend Satinderjeet Singh are accused of orchestrating the murder of a well-known Sikh independence activist, Hardeep Singh Nijjar, who was fatally shot outside a temple where he served as president in 2023. The murder sparked tensions between the Canadian and Indian governments, after then-Canadian Prime Minister Justin Trudeau said there were “credible allegations” that the Indian government was involved in the death of Nijar. Bishnoi is in custody, but Singh has not been arrested.

Bishnoi’s organization “routinely violently attacked prominent religious, social and political leaders” in exchange for large amounts of money.

Nijjar, who was 45 when he died, was a leading member of a movement to create an independent Sikh homeland known as Khalistan, and was organizing an unofficial referendum among the Sikh diaspora with the organization Sikhs For Justice. Nijjar, who was born in India and was a Canadian citizen, was wanted by Indian authorities at the time of his death. Authorities had offered a reward for information leading to his arrest.

Sikh diaspora activism has been a source of tension between India and Canada for years. Canada has the largest population of Sikhs outside India, and India has repeatedly accused it of tolerating “terrorists and extremists.” Both India and Canada expelled diplomats from the other country amid the international dispute.

Authorities also named two other criminal organizations that were arrested on similar charges over the course of the two-year investigation. Transnational organizations have members in countries ranging from the United States, New Zealand, Australia, Portugal and the United Kingdom. Members of the group are also accused of stealing large quantities of drugs from other criminal organizations operating in California and then selling the illicit merchandise throughout the country and in Canada.

The allegations say some defendants took advantage of relationships with corrupt local authorities in India to pursue rivals or those believed to be cooperating with law enforcement. At least one defendant is accused of organizing criminal activity while detained at an Immigration and Customs Enforcement facility, authorities said Tuesday, although it is unclear how he was able to communicate undetected.

No attorney for Bishnoi was listed Tuesday afternoon.

On Tuesday, authorities touted the operation as an example of international cooperation.

“Working together, law enforcement agencies in the United States, Canada, Europe and Asia are determined to target and dismantle these criminal organizations wherever they operate,” Essayli said.