"We will grieve with you. We will defend you. We will love you. And we will stand with you," Canadian Prime Minister Justin Trudeau said.
Trudeau's office sent a letter to Fox News on Tuesday, apparently aiming to keep that promise.
The letter was about a tweet Fox News published Monday that said the shooting suspect was "of Moroccan origin."
Authorities released the identity of the suspected shooter, who is French-Canadian, on Monday night. But Fox News still had the tweet online Tuesday afternoon.
Police had originally arrested two people. However, police determined one of the men was a witness.
The letter from Trudeau's office said the tweets "dishonour the memory of the six victims and their families."
It went on to say, "We need to remain focused on keeping our communities safe and united instead of trying to build walls and scapegoat communities."