OTTAWA, CANADA: Police stand guard in front of the National War Memorial one day after a gunman opened fire there, killing Canadian army reservist, Cpl. Nathan Cirillo. The gunman then entered the nearby main Parliament building, where witnesses say shots were fired -- many by security officers -- before he was shot dead, authorities said. 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 haven't provided any possible motives for the shooting. A U.S. law enforcement official told CNN that a connection to terrorism hasn'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. Photo by CNN's Khalil Abdallah, October 23. Follow Khalil (@madcameraman) and other CNNers along on Instagram at instagram.com/cnn.