OTTAWA — The Canadian police acknowledged on Thursday that the gunman who traumatized the capital in a deadly shooting rampage had not been identified as a security threat despite his criminal record in three cities, embrace of extremist ideas and intent to travel to Syria.

The police also conceded that they did not even know that the gunman, Michael Zehaf-Bibeau, had been in the capital for nearly three weeks.

The revelations at a news conference came a day after the gunman paralyzed the heart of the capital, killing a soldier at a war memorial before he was shot dead in the halls of Parliament.

The new detailed information helped fill in vast gaps about Mr. Zehaf-Bibeau’s surprise assault, including chilling video footage of his arrival on Parliament Hill.