10/23/2014 10:02 EDT | Updated 12/23/2014 05:59 EST

Ottawa shooting: Police rule out 2nd gunman as his mother cries for victims

Ottawa's police chief says investigators have ruled out a second gunman in yesterday's deadly attack on Parliament Hill as the precinct remains under tight security, with police cordons blocking traffic and snipers visible atop downtown buildings.

"We’re satisfied at this point one individual was responsible for the shooting yesterday on the Hill," Chief Charles Bordeleau told CBC News, following almost 24 hours of uncertainty as armed officers remain in control of the city core.

Meanwhile, the mother of the dead gunman, who was shot and killed within metres of a room where the prime minister was meeting with members of Parliament, told The Associated Press she is grieving for the victims of the attack, including a soldier doing honour guard duties. 

"Can you ever explain something like this?" Susan Bibeau said in a brief telephone call. "We are sorry."

Authorities have identified the gunman as Michael Zehaf-Bibeau, whose rampage with a hunting rifle in the Canadian capital was stopped when Parliament's sergeant-at-arms and RCMP fatally shot him in the marble hallway of Centre Block.

Ottawa Civic Hospital confirmed Wednesday that four people were taken to hospital: the soldier who died, and three who were released after treatment for minor injuries. 

Earlier this week, in a separate incident, a soldier was killed in Quebec when he was run over in a parking lot. 

Martin Couture-Rouleau struck two members of the military with his car in the St-Jean-sur-Richelieu lot, in what CSIS has described as "the violent expression of an extremist ideology."

Warrant Officer Patrice Vincent has since died. Couture-Rouleau was shot and killed by police following a high-speed chase as he fled the scene.