I think the case-the one case, it should be noted-you're using is one where the US authorities were unaware of his criminal actions. The Canadians weren't chasing him or trying to arrest him as he fled.

In this case, the Canadians were aware of the bad guys coming, and they knew the Americans were trying to stop them. Did they make any attempt to stop them? No, they left the border wide open, leaving the people stuck in the lines waiting to cross to fend for themselves.

You can't blame the Americans for not arresting a suspicious character and minimize the Canadians doing nothing- absolutely nothing - to detain or hinder two known murderers from crossing.

Crazed Rabbit