THE body of a young woman has been discovered in a lake – she is the victim of a brutal murder.

She is discovered by a walker, who reports apparent stab wounds, and on arrival police discover she has no shoes or jacket on, and bruising to her face.

Immediately they deem the circumstances suspicious and launch a major investigation.

In this instance the body is not real – it’s part of a scenario set up by Swindon’s Criminal Investigation Department to offer selected civilians an insight into their intriguing and often grim world – but the situation is all too realistic.

Murder is perhaps the most foul of all the crimes CID detectives face in their day jobs and nothing has put that into sharper focus than the high-profile killings of Sian O’Callaghan and Becky Godden-Edwards.

It is also resource intensive, with 100 officers from all levels typically involved on the first day of an inquiry, from forensic examiners through to intelligence cells to firearms officers.

Wiltshire Police have paired up with Avon and Somerset Police, under the Brunel collaboration, to share resources in major investigations.

Detective Chief Inspector Owen Gillard, head of the serious crime group, is keen to point out the level of teamwork involved.

“When you get something like Sian O’Callaghan’s murder it can have massive resource implications,” he said.

“You are taking officers from the front line of their regular jobs and using them in specialist roles.

“There were 150 investigators under a detective superintendent.

“Wiltshire Police handle the investigation in the first 24 hours until Brunel comes in to take over the long game of investigation.

“That first day will be crucial, with the first few hours after a crime known as the ‘golden hours’, in which as much evidence as possible is collected and vital intelligence sought.”

The scenario set up for members of Swindon Council, Wiltshire Fire and Rescue, police staff and domestic violence charity Splitz is designed to demonstrate exactly that.

The woman’s body had been found at Shaftesbury Lakes, which lies between the Parks and Eldene in Swindon.

This instantly throws up difficulties; How to recover the body? Where to place cordons to keep unnecessary people away from the crime scene? How to preserve evidence, the integrity of which may have been compromised by exposure to water?

Head of forensics Barbara Lockwood explained: “Water causes us huge problems. It really depends how long the body has been in the water.

“The primary question is who is this person, and the first thing detectives want to do is rifle through the pockets – that is a real no, no.

“It is our job to find out exactly what happened and we base it on facts and evidence, not on what we are told.

“We look for transfers, fibres, hairs and any DNA, and we photograph everything that is relevant.

“We only get one opportunity at it and, as because of that, the crime scene examination can take a whole day.”

Once the identity of the deceased is established detectives can follow tangible leads.

Victim Josephine Sara Allen, a 23-year-old mother-of-one, had been on a night out with her friend Becky the night before her death.

Becky revealed it was the first night out she and Josie had had since starting a new relationship with a man, known only as Ash. She also said she had noticed bruising on Josie’s face during a chance meeting in a supermarket weeks before.

In the nightclub Josie had received a call on her mobile demanding she return home immediately – it was Ash.

Towards the end of the first day, hundreds of hours of CCTV footage have been seized and are being monitored, while intelligence checks on Ash reveal he has a violent past and also turn up an address for him.

Armed officers then prepare to make an arrest, taking into consideration he is violent and working out the best way to gain access and apprehend him without compromising potentially vital evidence.

It isn’t case closed yet, but as a scenario DCI Gillard feels it is close to the pace of a real investigation. “Typically there would be 100 officers involved on day one, with large numbers of specially-trained officers who we draw in from their day jobs on the front line,” he said. “It was a realistic scenario – believable and realistic in terms of timings. By the end of the first day I would be hoping to make an arrest.

“You can see how we have to bring in people with so many different expertise, from forensic teams, to search teams to firearms.

“It might help to dispel the myth that it is just one person on the case, the senior investigating officer – the Inspector Morse.”

* Mini-cab driver Chris Halliwell, 47, of Ashbury Avenue, Nythe, is on remand charged with both Sian and Becky’s murders but has yet to enter any pleas.