Former detective Mark Williams-Thomas conducts an investigation into allegations that Sir Jimmy Savile sexually abused vulnerable teenage girls.

That Jimmy Savile fancied young girls is beyond doubt. He never married, and colleagues say he simply wasn’t interested in women over 20. As long ago as 2000, Louis Theroux was publicly raising the possibility that the shell-suited entertainer might be a paedophile. And yet, nobody wanted to know. Newspapers, politicians, the thousands of people who loved the saviour of vulnerable children, they all turned a blind eye.

Like MPs’ expenses and phone hacking, the Savile case is another example of a crime so familiar within its own industry that nobody thought to address it. Childline founder Esther Rantzen last week accused the world of TV, herself included, of “colluding” in a cover-up. Even as recently as last year, the BBC was so terrified of revealing that a national treasure, created largely by itself, was also a cold-hearted monster.

So, it’s fitting that the medium that made Savile has now destroyed him. I can’t remember the last time a TV documentary broke a major story, and former police detective Mark Williams-Thomas is to be applauded for conducting a thorough and level-headed investigation in Exposure: The Other Side of Jimmy Savile. He interviewed five women, whose allegations against Savile were startlingly similar: each spoke of a short, brutal encounter, either in his dressing room, or in a caravan, or in his car.

It made for depressing viewing, as each victim told her tale. There was no sensationalism: the unpalatable details spoke for themselves. It was a rare event in modern television: a documentary with no need for flannel or fancy camerawork. It was a straightforward piece of investigative journalism, a story the News of the World would once have prided itself on running.

All credit to Williams-Thomas for tracking down Savile’s victims and persuading them to go on the record. Since the programme aired, at least 11 women have come forward, and Paul Gadd, aka Gary Glitter, and a third celebrity have been accused of indecency. The pity is that Savile isn’t around to defend himself, but the similarity between the testaments has convinced experts on abuse that they are genuine.

Williams-Thomas’s documentary is only the beginning. Now, the BBC, investigative journalists, and everyone who knew about the rumours but failed to act must ask themselves why. The interviewed victims and colleagues all said that they were frightened of Savile, and that even if they did speak out, they wouldn’t be believed. If anything can be learned from this story, it’s that we ignore uncomfortable evidence at our peril. The trouble is, with each revelation of this kind, we lose a bit more trust in society, especially in those who work with vulnerable people.