I suppose it's like any other Criminal Code offence, in that the information would come to law investigators. It may be parents letting the authorities know that their children are getting on a plane to join a terrorist group somewhere outside of the country, so it may come from parents, but when the information comes to law enforcement agents, it would be investigated, as they do in other criminal offences, and a decision would be made at that time.
On November 19th, 2012. See this statement in context.