"Privacy watchdogs from across the country said this week that Canada’s spy agencies should destroy the data trails of innocent people they collect incidentally during terrorism investigations, once the actual targets have been cleared of suspicion."

This is not adequate.  From my experience of bizarreries when I was an employee of the House of Commons, I  believe that security agency investigations might involve advising third parties of suspicions about individuals.  As a consequence, those being investigated are liable to be treated prejudicially  by "patriotic" dupes, who have been fed a contrived scenario about a target person's disloyalty; e.g., in the case I am citing, medical care given the latter was apparently compromised.

Given the large numbers of security agencies' personnel, the need to develop "cases" for training purposes is enormous.  Yet falling victim can destroy the lives of unsuspecting innocents.

When they are exonerated, such people need to be so informed.