It's a staple of every bad prison movie you ever saw. Right after the beating scene comes the coverup scene. Some do-gooder demands to know, how come the prisoner is black and blue?

"Heck," drawls the warden, "he just fell down the stairs!"

Of course, there are variations on this timeless scenario. Sometimes, the warden says it with a straight face; sometimes, with a smirk to show that, sure, he's lying — but you can't prove it. Either way, the fell-down-the-stairs routine has become a B-movie cliché for good reason: it's grounded in reality. Stuff happens in prison. People get beaten. Witnesses are scarce. You can't prove it.

A case in point is a hapless, nameless Afghan prisoner who told his story to a Canadian visitor in 2007 but whose identity, age and offence are all hidden behind a wall of censorship. Even so, his case became known in Canada in November of 2009, thanks to the testimony of diplomat Richard Colvin before a parliamentary committee.

While serving in Afghanistan, Colvin said, he warned his superiors that prisoners captured by Canadian soldiers were routinely tortured by the Aghan National Directorate of Security, the NDS. Colvin told the committee that a new, tougher agreement with the Afghan government, signed in May of 2007, failed to fix the problem.

"Some of our detainees continued to be tortured after they were transferred," said Colvin. "As I learned more about our detainee practices, I came to the conclusion that they were contrary to Canada's values, contrary to Canada's interests, contrary to Canada's official policies, and also contrary to international law, that is, they were un-Canadian, counterproductive and probably illegal."

Colvin cited the nameless prisoner above who, he said, told a Canadian monitor "that he had been tortured, showed him the marks on his body, was also able to point to the instrument of torture which had been left under a chair in the corner of the room by his interrogator."

The story was borne out by the official documents that were revealed at an inquiry by the Military Police Complaints Commission. In a diplomatic field report from November of 2007, the detainee's story of his time in an NDS prison is laid out:

"...he could not recall the first interrogation in any details as he was allegedly knocked unconscious early on. He alleged that during the second interrogation, 2 individuals held him to the ground with his shawl while the other 2 were beating him with electrical wires and rubber hose. He indicated a spot on the ground in the room we were interviewing in as the place where he was held down. He then pointed to a chair and stated the implements he had been struck with were underneath it. Under the chair, we found a large piece of braided electrical wire as well as a rubber hose. He then showed us a bruise (approx 4 inches long) on his back that could possibly be the result of a blow. While we did not ask, after the interview was completed and before we left, [a senior official] told us that....[REDACTED.]

Told us ... what? What's redacted? We're not supposed to know that. In the version released this week by two eminent jurists, the rest of the sentence is blacked out.

And rightly so, the judges say. In their new report, commissioned by the last Parliament after a heated showdown over documents and censorship, retired Supreme Court Justices Frank Iacobucci and Claire L'Heureux-Dubé explain that the law requires them to conceal anything which could undermine national security or international relations.

So we must never know what the "senior official" from NDS told the Canadian visitor to that prison — right?

Wrong. Despite the judges' best efforts, it's really no secret. It's been public for more than a year, without a murmur of complaint from government lawyers, in the version released at the Military Police Complaints Commission. And here is what that Afghan security official said:

"...that the detainee had allegedly fallen on the steps the other day..."

Ah. The old fallen-on-the-steps story. But what does that have to do with national security? Or international relations? It's hard to tell. Did the two judges decide that folks might think less of our Afghan allies if it were known that they offered such a lame excuse?

Perhaps — although that theory is hard to square with the fact that the same judges had no problem revealing evidence that Afghan officials routinely tortured prisoners. On the scale of wickedness-that-must-not-be-revealed, the torture would seem to be rather more damaging than the excuses.

Still, the "international relations" exception seems to be extremely flexible. Ditto, "national security." In fact, the definition of what's important to censor and what isn't seems to be both flexible and constantly shifting. In another baffling example, there's a document which says a prisoner was deprived of sleep for [X] days. We must not know how many days! And, yet, we do! In another version of the same document, we can see that it was ... four days. Somehow, the national security of both Canada and Afghanistan seems unaffected by this revelation.

In the case of the prisoner victimized by the stairs — or by the rubber hose and the braided cable — we have no clue what the judges were thinking. Perhaps they did not know that the document was already public and thought no one could second-guess their decision to censor it.

Or maybe, after long years on the bench, they were just heartily sick of the hackneyed tale of the prisoner who'd "fallen on the steps" — and didn't want to inflict it on anyone else.