"We're all troubled by the fact that a Canadian has been in a Mexican prison now for two years without trial," [Stephen Harper] said following an event at an elementary school in London, Ont.

Harper said the government at all levels, up to and including cabinet, has worked diligently on the file since [Brenda Martin]'s arrest in early 2006. Still, Harper cautioned he wasn't making excuses when he said he can't simply pick up the telephone and demand Mexico's president release her.

"A judicial processes is, by definition, independent," Harper said. "If the president of Mexico called me and demanded I release a Mexican national, I would not be in the position to do that."