Madness in the Fast Lane, BBC One

Words such as horror, grotesque, shocking and bizarre are fired at us before the title has even appeared on screen: clearly this documentary is set on living down to its sensationalist title. One bleak sunless day in May 2008, Swedish twins Sabina and Ursula Eriksson ran into traffic on the M6. Both miraculously escaped with their lives but then turned on the police officers trying to help them. With a lack of subtlety and restraint typical of this kind of schedule-filler, director Jim Nally shows us the footage of Sabina being thrown off the bonnet of a car at least twice more, slowing it down, freeze-framing it, and then just flashing up fragments of it - hammering home the kind of imagery which will have stuck in the mind of any sensitive viewer anyway.

Madness in the Fast Lane was, if anything, Unreality TV. The story being told was so weirdly random, banally horrible and lacking in narrative logic that it would never have passed muster as fictional drama. But of course while certain aesthetic and moral aspects of the film might be down to the director, the events that unfolded were not. Real life doesn't always conform to the kinds of expectations we have of fiction.

For example, when the police tried to help the injured twins they were punched and spat at rather than thanked. One twin shouted out, “They’re going to steal our organs!” The other broke free from her captors only to run straight back into the traffic. And when Ursula was hospitalised with multiple fractures, her sister didn’t even ask the authorities about her condition. She seemed more interested in flirting and checking that she looked okay on camera.

A fictional drama would also have required Sabina to attempt to passionately defend her actions of a couple of days later when, having been released from police custody, she randomly murdered a local man who was trying to help her.

But she refused to talk about the event at all: Cracker would have just thrown his arms up in exasperation and gone off to the betting shop. So the twins must have been drunk, on drugs, or driven insane by abusive relationships, one might suppose, still floundering around for reasons or justifications for their behaviour. But no, pretty much any explanation that might have been seized upon by a lazy scriptwriter is a dead end in this baffling story, which was told with a collage of CCTV footage, blurrily convincing reconstructions and footage filmed by cameramen working on the BBC series Motorway Cops.

This whole sorry mess got even messier and sorrier by the end, when we were finally told that Sabina’s condition was a temporary aberration and that she is up for parole on her five-year sentence for manslaughter next year. Why wasn’t this woman’s mental health properly analysed following the motorway incident? And should she even have been imprisoned in the first place given the fact that the motiveless murder was clearly a further symptom of the same condition which sent her running off into motorway traffic? And given that one expert said her symptoms could return, should she really be allowed back into the community?

While this 50-minute film presented the facts, I do feel a more analytical investigative documentary could still be made about this stranger and scarier than fiction case.

• Watch Madness in the Fast Lane on BBC iPlayer