A 27-year-old man has been identified as the lone suspect in a mass shooting at a Quebec City mosque, where six were killed and five others critically injured during evening prayers on Sunday.

Alexandre Bissonnette of Quebec City was charged with six counts of first-degree murder and five counts of attempted murder on Monday. The suspect said nothing and only stared at his feet during his first court appearance. In an afternoon press conference, an RCMP spokesperson said that additional terrorism-related charges may be forthcoming.

Vigils for the slain men were held across the country on Monday, drawing scores of mourners.

“I think it’s necessary for the Muslim community to feel accepted here in Quebec,” Emma Larochelle told CTV News Channel from a vigil in front of the crime scene, the Centre Culturel Islamique de Quebec. A friend of Larochelle’s had left the place of worship just before the attack began.

“I think it’s a good thing for me to be here to show support to my friends because it’s a small town and we know a lot of people that were affected by the attack, that had some family in there or were just there before the attack… The whole day I was trying to find something to say and maybe show my support, and I think the best way I could find was to come here tonight.”

Bissonnette was arrested along with one other individual following the shooting, which began shortly before 8 p.m. Sunday in Quebec City’s Sainte-Foy neighbourhood, when a masked gunman allegedly stormed the mosque’s main floor and began shooting at random.

The gunman fled the attack by car, only to call police several minutes later to turn himself in.

According to Surete du Quebec, the second person who was arrested is being treated as a witness.

The Department of National Defence confirms that Alexandre Bissonnette was a cadet between 2002 and 2004 in the Quebec City area. He was an air force cadet briefly in 2002, then an army cadet. Cadets are not members of the Canadian Armed Forces and they do not receive military training.

Laval University, a French-language public university in Quebec City, has confirmed that Bissonnette was a student at the institution’s Faculty of Social Sciences.

The six people killed in the attack included a professor and a grocery store owner. Police say the victims were all men between the ages of 39 and 60. Five victims were also taken to hospital in critical condition -- three remain in intensive care while the other two were in critical but stable condition, a hospital spokesperson said. Fourteen others suffered minor injuries.

As police continue to investigate and conduct raids, authorities are asking for members of the public to come forward with any information that might help with the case.

Patrick Lalonde, assistant director of the Service de Police de la ville de Montreal, says security has been increased around mosques in the area. "We have asked for all our police officers to increase the levels of vigilance and surveillance around mosques and other community services," he said at a news conference Monday morning.

Prime Minister Justin Trudeau and Quebec Premier Philippe Couillard both condemned the incident as a terrorist attack.

"It is heart-wrenching to see such senseless violence," Trudeau said in a statement. He also offered his sympathies to the victims and his support to Canada's Muslim community. "Diversity is our strength, and religious tolerance is a value that we, as Canadians, hold dear," he said. "Muslim-Canadians are an important part of our national fabric, and these senseless acts have no place in our communities, cities and country."

Trudeau repeated his condemnation of the attack in the House of Commons Monday afternoon, where he again called it a "terrorist attack." He is slated to visit Quebec City later in the day, along with Rona Ambrose, interim leader of the Conservative Party, and Thomas Mulcair, leader of the NDP.

"We must stand united," Trudeau said. "Senseless violence has no place in Canadian society."

Premier Couillard urged Quebecers to stand in solidarity with the Muslim community. "Let us unite against violence," he tweeted in French. 

"This is your home, you're welcome here," Couillard said at a news conference, speaking to the Muslim community. "We are all Quebecers."

Public Safety Minister Ralph Goodale later told reporters that the motivation for the attack is not known, but that it meets the “broad definition” of a terror attack.

He said Canada’s terrorism threat level remains at medium, where it has stood since October 2014.

Quebec City Mayor Regis Labeaume said the city is in mourning. "We have the impression we are dreaming," Labeaume said at a news conference Sunday night. "I have often said in recent weeks that, despite the peace we have here, we are not immune (to attacks). Well, this has just proven that."

Video from the scene shows several police cars outside the mosque on Sunday night.

Vigils are planned at mosques in several parts of the country, including Quebec City and Montreal.

Members of the Muslim community have condemned the attack, with many calling for tighter security around other mosques in the country.

"We are horrified by this despicable act of violence," Ihsaan Gardee, executive director of the National Council of Canadian Muslims, said in a statement. "This act of wanton murder must be punished to the fullest extent of the law."