The alleged shooting at Rideau never took place by all accounts from authorities. There was only one shooter involved today. He shot Cirilo at the war memorial then drove his car a short distance up Wellington and parked outside East block, walked up to the Centre Block and opened fire once inside where he was killed by Srgt at arms Vickers and his staff.
There's no indication of any other shooters, but police and RCMP are searching much of the downtown core and clearing them from lock down. It's also important to note that most of Parliament and the War Memorial are a crime scene right now.
The security level has been raised on the Hill over the past few days so it seems they had perhaps expected something and now are taking lots of precautions. Who knows what kind of threats they've received so anything given the current situation need to be taken very seriously.