Abdulahi Hasan Sharif, a 30-year-old refugee from Somalia, arrived at a border checkpoint in 2012 and "requested asylum from Canada," Immigration Minister Ahmed Hussen said.
"He went through the regular process at that time and he was granted refugee status later that year," he said.
US Immigration and Customs Enforcement (ICE) revealed that Sharif had been detained for four months in San Diego, California in 2011 and ordered removed to Somalia by an immigration judge.
ICE spokesman Lauren Mack said in an email to AFP that Sharif had waived his right of appeal and was released on November 23 of that year "due to a lack of likelihood of his removal in the reasonably foreseeable future."
Two months later on January 24, 2012, however, he failed to report to authorities for removal and efforts to locate him were not successful, Mack said.
Prime Minister Justin Trudeau, responding to questions about why Sharif was granted asylum when he likely should have been turned away under Canadian law, said: "We are looking into exactly what happened in this situation, but it's certain that we have asylum processes that needed to be followed rule by rule."
"We're looking into the whole system and we'll reflect on whether we need to do things differently in the future than the way they were done in 2012," he added.
Under a 2004 Canada-US agreement that seeks to discourage so-called asylum shopping, applicants must file a refugee claim in the first country in which they land.
Thus Sharif would have had to make a refugee application in the United States, although some exemptions under exceptional circumstances may be granted, according to immigration officials.
Sharif appeared Tuesday in an Edmonton court where he was charged with five counts of attempted murder and related offenses.
Subsequent proceedings have been delayed until the defendant obtains a lawyer.
The Royal Canadian Mounted Police (RCMP) anti-terrorism squad took over the investigation from the Edmonton police after an Islamic State group flag was discovered in the suspect's car.
While the prime minister himself also denounced the act as a "terrorist attack," no terrorism charges have been laid in the case.
RCMP Superintendent Stacey Talbot said this week that the investigation was still in its infancy, but added that "if warranted, further charges will be pursued."
Late Saturday, the suspect drove his car into a barrier outside an Edmonton football stadium and struck a policeman directing traffic. He then jumped out and tried to stab the officer, who fought him off with one hand.
Hours later, the suspect took police on a wild chase through the city's downtown in a rented van as he tried to mow down pedestrians on a street with several popular bars and nightclubs, before the vehicle was knocked over and the driver was apprehended.
A police scanner recording posted on Live Leak revealed those frantic moments: "He's hitting pedestrians here," says an officer. "Guys we need to take that vehicle right now."
"Use all means necessary to stop that vehicle and end this flight," comes a reply.
The injured officer and two of the four pedestrians have been released from hospital.
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