Belgian authorities are facing embarrassment after Turkey said on Wednesday that last year Ankara expelled back to Europe Brahim El Bakraoui.
A Raleigh, North Carolina, police officer on Monday killed a man who was fleeing arrest, the authorities said.
The Belgian prosecutor has confirmed reports of the find in searches after November 13.
Officers had taken into custody four of the suspects, aged between 14 and 17, by Sunday night.
"There are no words to describe this tragedy where three colleagues have lost their lives."
ISIS claims the attackers were followers of the militant group.
A driver careened into the parade at around 10 a.m. local time.
Police believe Roof killed nine at a African-American church.
Britain's most high-profile Islamist preacher has rejected suggestions he influenced the Ottawa gunman, but warned there could be similar attacks in the UK
The 16-year-old girl is suspected of trying to join Islamist rebels in Syria