The violent weekend attacks in Edmonton that saw a police officer stabbed and pedestrians run down in the streets do not prove the immigration system failed, an Edmonton lawyer says.

Current screening processes for convention refugees are already extremely strict, said Ruth Williams, a lawyer with Legal Aid Alberta who specializes in refugee claims.

"The officers doing the screening are incredibly diligent. If there is a rock to turn over, they would turn it over," Williams said in an interview with CBC Radio's Edmonton AM.

"They don't have a crystal ball, they can't predict what people are going to do in the future."

Somali refugee Abdulahi Hasan Sharif, 30, has been charged with five counts of attempted murder, four counts of criminal flight causing bodily harm, and one count each of dangerous driving and possession of a weapon for a dangerous purpose. He remains in custody after making his first court appearance Tuesday.

Sharif is a Convention refugee, which means he was granted refugee status due to a fear of persecution based on race, religion, nationality, political opinion or membership in a minority group.

He was ordered to be deported from the United States in 2011 by a U.S. immigration judge.

In July 2011, U.S. Customs and Border Protection transferred Sharif into the custody of U.S. Immigration and Customs Enforcement (ICE) at Otay Mesa Detention Center in San Diego, Calif.

Two months later, an immigration judge ordered Sharif removed to Somalia. Sharif waived his right to appeal that decision.

He was released on Nov. 23, 2011, on an ICE order of supervision, but failed to report back to immigration officials and efforts to find him were unsuccessful.

end of police chase

Sharif was arrested after a dramatic pursuit by Edmonton police through downtown Edmonton. (CBC)

'Process ... incredibly strict and stringent'

Sharif crossed the border into Canada in 2012, and was granted refugee status in the same year.

Though targeted in a probe in 2015 for promoting extremist ideology, Sharif was deemed to pose no threat after an RCMP investigation.

Despite Sharif's history, there is no proof that reforms to immigration screening procedures are needed, Williams said.

It's not unusual for prospective refugees who have been rejected in the U.S. to seek residency in Canada, Williams added.

"The process that they have is incredibly strict and stringent," said Williams, who has been helping refugee claimants in Edmonton since 2010.

"I don't see how you could get any more stringent without trying to read people's minds."

'I don't see how you could get any more stringent without trying to read people's minds.' - Ruth Williams, lawyer with Legal Aid Alberta

Public Safety Minister Ralph Goodale said it would be wrong to blame the attack in Edmonton on any shortcomings in Canada's immigration and refugee vetting system.

Goodale said Sharif arrived through a "regular port of entry" and obtained refugee status. At the time, Immigration officials had no reason to red flag Sharif, Goodale said.

"There's absolutely no evidence of that whatsoever. The investigation is ongoing, but that conclusion is just not supported by the facts," Goodale told reporters in Ottawa.

Effort to tighten laws stymied, Kenney says

The immigration minister at the time, Jason Kenney, said he tried tightening security screening at the borders but was thwarted by the Obama administration, the Liberals, NDP and the courts.

"We did more than any government in history," said Kenney, who was immigration minister from 2008 to 2013 and is now a leadership candidate for the United Conservative Party in Alberta. "I was attacked by the Liberals and the NDP for the changes that we made.

"Unfortunately some of those things … have been struck down by the courts."

He said he also tried strengthening the Safe Third Country Agreement which prevents refugee claimants in the U.S. from seeking refuge in Canada.

"I fought to have it changed, the Obama administration refused."

Trudeau says Sharif's entry under review

Prime Minister Justin Trudeau said Wednesday the federal government is reviewing the circumstances around Sharif`s entry into Canada.

"We're certain that we have asylum processes that needed to be followed when someone presents themselves at our border, we have rules to follow and we make sure those rules are followed," Trudeau told reporters.

"We're looking into the whole system and will reflect on whether we need to do things differently certainly in the future than the way they were done in 2012."

Williams said prospective refugees are subject to numerous layers of vetting by national security officials before they are granted Convention status.

After an initial application is filed, refugees submit fingerprints and paperwork, and are subjected to extensive background checks and interviews, she said.

Claims must be well documented

Claims of persecution must be well documented or they will be rejected and, under the current regulations, applicants only get one chance to prove themselves.

Anyone with past criminal activity or convictions would be rejected outright, Williams said.

If Sharif is convicted, attempts will be made to deport him after his sentence is served, Williams said. In the meantime, she said she hopes other refugees don't bear the brunt of the blame for Saturday's attacks.

Canada's Convention refugee process saves lives, she said.

"I do worry that they will be more on the receiving end of this, which makes it all the more difficult because the average Canadian doesn't know what happens in the refugee process," Williams said.

"These are people that are basically fighting to save their lives and give themselves a future."

Listen to Edmonton AM with host Mark Connolly, weekday mornings at CBC Radio One, 93.9 FM in Edmonton. Follow the morning crew on Twitter @EdmAMCBC