( CNN ) The suspect in Wednesday 's shootings in Ottawa had `` connections '' to jihadists in Canada who shared a radical Islamist ideology , including at least one who went overseas to fight in Syria , multiple U.S. sources told CNN on Thursday . American officials are searching databases and communications for any links to American-based jihadists , law enforcement officials said . They spoke the same day Canadian lawmakers returned to work after the shootings , giving a standing ovation to the ceremonial Parliament official credited with taking down the gunman who killed a soldier and shook the Parliament area . The legislators ' return came as the country tried to come to grips with the second killing of a soldier on home soil in three days , and questions as to why the attacks came and who exactly was behind them . `` We 'll be vigilant , but we will not run scared . We will be prudent , but we will not panic . And as for the business of government , well , here we are -- in our seats , in our chamber , in the very heart of our democracy , '' Canadian Prime Minister Stephen Harper told the House of Commons in Ottawa on Thursday morning . Lawmakers stood and cheered Sergeant-at-Arms Kevin Vickers , who officials say took down the suspect in the halls of Parliament minutes after the killing of Canadian army reservist Cpl . Nathan Cirillo at a war memorial nearby . Vickers , who regularly leads a procession into the House as sessions begin , stood with his ceremonial mace and appeared to be emotional during the ovation . It was a step toward normalcy for a government district that was widely locked down for hours after the shootings at Canada 's National War Memorial and Parliament Hill . Authorities say a man shot and killed Cirillo , who was standing guard at the war memorial on Wednesday morning . The gunman then entered the nearby main Parliament building in downtown Ottawa , where witnesses say shots were fired -- many by security officers -- before he was shot dead , authorities said . A plainclothes constable who was working security at Parliament was shot in the leg , according to a House of Commons official briefed on the investigation . The injury is not life-threatening , and the constable was treated at a hospital and released , the official said on condition of anonymity . The gunman was Quebec native Michael Zehaf-Bibeau , a convert to Islam , U.S. officials told CNN , citing information given to them by Canadian authorities . Canadian investigators have n't provided any possible motives for the shooting . A U.S. law enforcement official told CNN that a connection to terrorism has n't been ruled out . The shootings left government workers and others locked inside offices for a large portion of the day while police searched buildings to ensure that no other culprit was loose . Wednesday 's deadly attack was the second on Canadian soldiers this week . On Monday , a convert to Islam who Canadian authorities said was `` radicalized '' hit two soldiers with a car in Quebec , killing one of them . Police later killed the man . `` When faced with attacks on the country we all love ... I know we will always stand together , '' Prime Minister Harper said Thursday . `` Canadians will not be intimidated . '' The suspect . Canadian authorities had confiscated Zehaf-Bibeau 's passport when they learned he planned to go fight overseas , a U.S. law enforcement official told CNN 's Susan Candiotti . The official said it was not clear when that happened . Zehaf-Bibeau , who was born as Michael Joseph Hall in 1982 , had a history of drug use before he converted , two sources said . `` In the days to come , we will learn more about the terrorist and any accomplices he may have had , but this week 's events are a grim reminder that Canada is not immune to the types of terrorist attacks we have seen elsewhere in the world , '' Harper said Wednesday . Police are satisfied that only one person was responsible for Wednesday 's shootings , Ottawa Police Chief Charles Bordeleau told Canadian media outlet CTV News on Thursday morning . Lawmakers pay respects to soldier . Before Parliament reopened , lawmakers gathered outside the memorial -- some holding flowers -- for a moment of silence for Cirillo . `` This was very off the cuff , '' lawmaker Charlie Angus told CNN on Thursday morning . `` I think parliamentarians really just felt that before we walked into the Parliament buildings , we had to pay respect to a young man who gave his life for his country . '' Angus said the soldiers ' killings this week left the government with plenty of questions . `` The questions we need to ask ourselves ( include ) , 'How are these people getting this crazy ideology that 's inspiring them to do these copycat killings ? ' `` he said . Another question , he said : What can society do to deal with people who find themselves on the fringes ? Issues of mental health , he said , need to be addressed . `` We can not let people like this fall through the cracks and end up doing deranged killings , '' Angus said . CNN 's Ashley Fantz , Josh Levs , Catherine E. Shoichet , John Newsome , Pamela Brown , Dana Ford , Elise Labott , Jim Sciutto , Pam Brown , Ana Cabrera and Deb Feyerick contributed to this report .
NEW : U.S. officials searching databases and communications for possible clues . A plainclothes constable detailed to Parliament was shot in the leg , official says . Canadian army reservist Cpl . Nathan Cirillo was killed at the National War Memorial . Lawmakers give standing ovation to Parliament official credited with stopping gunman .