FATAL road crashes can shatter families in an instant and piecing together exactly what happened can be extremely difficult.

But for Wiltshire Police’s Serious Collision Investigation Team, the detectives of the road, reconstructing the anatomy of horror crashes can at least help answer questions for the people left behind and at best hold someone to account for actions that robbed them of their loved one.

The unit, based at Devizes Police Headquarters, leads all investigations into crash deaths, such as that of 22-year-old Kanak Al Islam near Liddington last Wednesday, and life-threatening incidents, including most recently where a bus hit a nine-year-old boy in Swindon on Friday.

On Tuesday, the unit secured the conviction of Paula Barnes, 45, of Baydon, who caused the death of primary school teaching assistant and mother-of-two Diane Wright by dangerous driving.

Barnes, who went on the run in Holland for 17 months, had been twice the legal drink drive limit and was speeding on the wrong side of the road when her Audi smashed head-on into Mrs Wright’s BMW.

It was the expert roadside analysis of SCIT officers, who were on hand in the immediate aftermath of the incident, that led to her being jailed for eight years and five months.

Sgt Chris Moore, who has been with the unit since it was formed in 2009, said it was their job to get the answers for the families of crash victims.

He said: “The family always want to know more, to know how it happened and I always say we may not have all the answers but we will do the best we can.

“When we turn up to a scene we don’t know if we are dealing with a road traffic collision or a murder – we have to ask the question ‘was this a deliberate act?’.

“The first thing we must do is close the road as we only have one chance. We have a small window because as soon as you open the road, everything is lost.

“The forensic collision investigator, vehicle examiner and senior investigating officer must be at the scene, while logistically if we can get a family liaison officer there too then we will, as it gives them a better understanding.

“The CI will do all the physics and clever bits, while the VE will examine the cars in situ before they are recovered, and then again in more detail in the garage.

“The family liaison officer has perhaps the most difficult task – dealing with the families and the emotions they are struggling to deal with.

“It can be difficult emotionally sometimes, particularly where children are involved and it is close to home, but professionally you are focused on what you need to do.”

PC Bob Eccleston, an experienced CI who worked on the Barnes case, said officers used standard surveying equipment and physics and mathematics to build a forensic reconstruction of the crash.

He said: “We use a theodolite and general surveying kit to forensically assess the scene and record whatever marks we think are relevant, as well as damage to vehicles that would help us obtain, mathematically or physically, what happened.

“We can work out, if the parameters permit, what speed they were going and whether the brakes were applied through the distension on the brake light bulbs.

“We can get the recovery firms to put the vehicles back to the point they collided – they won’t fit together exactly but we can inspect the impact marks and the force of the impact will create gouges in the road surface.

“Using standard mathematical equations and physics we can give an opinion on what happened. It’s not an exact science but the mathematical models put us in the right ball park. We are the detectives of the road.”

Last year SCIT, comprised of one sergeant and 15 constables, dealt with 21 deaths on the roads in Wiltshire – and tragically, many could have been avoided.

Both PC Eccleston and Sgt Moore stressed that it was drivers themselves who were responsible for the majortiy of serious road crashes.

“In my experience, most incidents are down to driver error,” PC Eccleston said.

“A lot is said about speeding, which is an emotive subject, and there is also impairment or distraction.

“Drug and drink driving are a problem, with drug driving on the increase.”

Chris added: “In all my service I have only had one incident where a mechanical defect played a part.

“I think one major problem is people getting distracted by mobile phones – we had one conviction of death by careless driving recently where a man was on hands-free and collided head-on with an Astra coming round a bend.

“Tests show you are 12 times more likely to have a collision if you are on a mobile phone.”

While a prosecution cannot bring a family member back from the dead, it can at least soothe the anguish to know the person responsible has been held accountable.

“When families come up to you at the end of the court process and say ‘thank you’, that’s what makes it all worthwhile,” said Sgt Moore.