Madness In The Fast Lane BBC1

THE French have a name for it – folie à deux, "a madness shared by two". Then again, it might have been bouffé délirante, "a puff of madness". The family and friends of Glenn Hollinshead, one imagines, care little for such psychological intricacies. All they know is that whatever consumed Sabina Eriksson resulted in the violent death of a much-loved good Samaritan, a man who, tragically, lost his life for the belief that man should not simply pass by on the other side.

It was 2008 when Swede Sabina and twin sister Ursula ran out into traffic on the M6 near Keele. Ursula disappeared beneath the wheels of a 40-tonne truck. Sabina's imprint was left on the windscreen of a car. The footage has been shown before on Motorway Cops. But it was heavily edited. For legal reasons, the programme couldn't reveal what followed. Like the moment, with hindsight chilling in the extreme, when Sabina casually tells an officer: "We say in Sweden that an accident rarely comes alone. Usually at least one more follows – maybe two."

Within 24 hours, Sabina had stabbed Fenton man Glenn to death, before repeatedly smashing herself on the head with a lump hammer and hurling herself 40ft from a bridge on to the A50. To be honest, if Madness In The Fast Lane was a drama, you'd turn over, convinced it was way too far-fetched.

Sabina has never given a reason for her actions. All we know is that, as she first lay prone, and then rose, with startling strength, from the road, she shouted: "They're going to steal your organs," to bemused motorists. "I recognise you – I know you're not real," she also told a police officer.

It was a level of paranoia witnessed later by Glenn's friend Peter Molloy, spooked by Sabina's demeanour after she approached himself and Glenn as they walked home from a pub in Fenton. "This is beyond weird," he thought. "There's something not right about this woman."

Glenn's family are understandably angry that Sabina was so easily released back into society after the Keele incident. "It's the behaviour of two people who are clearly very, very disturbed mentally," said brother Garry. "These people need to be held and assessed very, very thoroughly both for their protection and the public's protection."

"To say someone is fit after that," adds brother Paul. "I just couldn't believe it."

Staffordshire Police, meanwhile, point to the fact that Sabina had calmed hugely in custody. She was seen, they say, by several health professionals before being passed fit.

The family's grief is further stained by the fact that Sabina was sentenced to just five years imprisonment, after admitting manslaughter on the grounds of diminished responsibility.

It was claimed in court that, while she was mentally ill at the time of the offence, she was not so at the time of sentence.

"I think it's very nice that they've got a future," said Paul of an outcome that has virtually no legal precedence. "Off they go, happy families, while our family's left in limbo. I miss Glenn to bits."

And he added a final fear that must nag all concerned with this case. "If she's in contact with her sister," he pondered, "who's to say it wouldn't trigger it all over again?

"If it did happen again, there'd be a lot of questions to be answered."