A Sikh extremist invited to a dinner reception with Prime Minister Justin Trudeau in India this week was once accused of attacking a former B.C. premier. Ujjal Dosanjh said the Canadian government demonstrated a lack of concern by inviting the man – convicted of attempted murder in another case.

Mr. Dosanjh, also a onetime federal Liberal cabinet minister, says he was taken aback when he found out that Jaspal Atwal was invited to a Thursday night dinner reception with the Prime Minister after attending another event with the Trudeau family earlier this week. Mr. Dosanjh says Mr. Atwal attacked him with an iron bar in 1985 over his opposition to Sikh extremism. The attack left him with 80 stitches and a broken hand. Mr. Atwal was acquitted of the attack.

"It left me speechless about the lack of preparation or the depth of unpreparedness with which Mr. Trudeau's trip went through," Mr. Dosanjh said.

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"It wasn't the best [decision] both from a security point of view and from the political perception point of view for Indians. It was absolutely mind boggling."

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Mr. Atwal was a member of the International Sikh Youth Federation, which is deemed a terrorist group in Canada and India, when he was convicted of the attempted murder of Indian cabinet minister Malkiat Singh Sidhu in 1986. Mr. Sidhu was wounded in an attack.

Speaking to media in India on Thursday, Mr. Trudeau said Mr. Atwal should never have been invited to the dinner at the Canadian High Commissioner's residence in Delhi, rescinding the invitation. But Mr. Atwal had already gained access to the Canadian delegation. Photos obtained by CBC News show Mr. Atwal posing with Mr. Trudeau's wife, Sophie Grégoire Trudeau, and Liberal Infrastructure Minister Amarjeet Sohi at an event in Mumbai on Tuesday.

Mr. Trudeau said Liberal MP Randeep Sarai invited Mr. Atwal to Thursday's dinner reception. Mr. Sarai is one of 14 MPs on the Prime Minister's trip to India.

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"Obviously we take this situation extremely seriously," Mr. Trudeau said.

"The member of Parliament who included this individual has and will assume full responsibility for his actions."

In a statement, Mr. Sarai said he facilitated Mr. Atwal's request to attend the event at the High Commissioner's residence. He said he should have exercised better judgment and apologized.

Reached by phone Thursday, Mr. Sarai hung up on The Globe and Mail when asked to explain why he invited Mr. Atwal to the dinner reception.

After initially pointing the finger at Mr. Sarai, the Canadian government later spread the blame to "factions in India" it says may have orchestrated the Atwal matter.

In an interview late Thursday night, a senior government source said the Indian factions in question are concerned about the threat of Sikh extremism, especially among the Sikh diaspora in Canada, and believe that the Canadian government is too complacent on the matter. The source did not say whether said factions were linked to the Indian government.

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Reliable sources also said Mr. Atwal was removed from a blacklist of people banned from India several months ago and that Canada played no role in removing him from the list. The sources said any further questions about how Mr. Atwal got into the country should be directed to Indian authorities.

In a tweet Thursday, Conservative Leader Andrew Scheer accused Mr. Trudeau of "wining and dining" an attempted murderer.

"Just outrageous. Justin Trudeau has, once again, failed to show the basic judgment required of a leader," Mr. Scheer tweeted.

Former RCMP investigator Garry Clement said the Atwal incident raises security concerns. Mr. Clement, who once worked as the RCMP liaison officer at the Canadian mission in Hong Kong, said every embassy and high commission vets visitors when parliamentarians or senior government officials are visiting. However, he said the Prime Minister's Office does not have to follow the RCMP's advice.

"I can tell you that I experienced several occasions where the VIP opted to ignore our advice," Mr. Clement said.

"The PMO, they can do a lot of push back on these things. I ran into it several times".

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Asked whether the PMO sought the RCMP's advice on Mr. Atwal, spokesperson Eleanore Catenaro said the office does not comment on matters relating to the Prime Minister's security.

NDP Leader Jagmeet Singh said there are a lot of questions about how Mr. Atwal was allowed into India while others, including him, have been barred entry to the country for speaking out about human rights. He said he condemns all acts of terrorism and violence, while maintaining a belief in the freedom of expression.

"We should be wary of any international interference in our political affairs especially when its targeted at minorities such as members of the Sikh community. The Indian government has a troubling record of conflating human-rights advocacy with extremism for their own political benefit," Mr. Singh said.

Former Canadian ambassador Ferry de Kerckhove said the Atwal matter gives the impression that Mr. Trudeau does not take security as seriously as he maybe should.

"It is very, very unfortunate because it can only heighten the concern of [Indian Prime Minister Narendra] Modi towards the commitment of Canada to fight Sikh terrorism in Canada," Mr. de Kerckhove said.

Mr. Trudeau, who is scheduled to meet with Mr. Modi on Friday, has already spent part of his trip trying to persuade India that his government does not sympathize with Sikh separatists. During a meeting with Punjab Chief Minister Amarinder Singh Wednesday, Mr. Trudeau said Canada supports a united India and would look into concerns that financing for Sikh separatists is coming out of Canada.

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Another former Canadian ambassador, David Mulroney, said the Canadian government will continue to be "susceptible to embarrassing situations like the Atwal invitation" if it keeps seeing its relationship with India "through the prism of diaspora politics."

"There are a number of serious human-rights problems that the Prime Minister should raise with India, including concerns about all religious minorities. Doing this solely on behalf of a community that has political clout in Canada is wrong and inevitably entangles us, inappropriately, in India's domestic politics," Mr. Mulroney said.

With a report from The Canadian Press