Robbie Coltrane's Critical Evidence

Cycling through the countryside on a clear December morning in 2002, an off-duty fireman smelled burning flesh. In the distance, he could see a body smoldering in a field. The police arrived to discover the body was charred beyond recognition; all they knew is that the man had died a brutal death, his killer or killers having stabbed him repeatedly, shot him in the head, and drenched his body with petrol before setting it alight.

For the first time on British television, we're telling the story of this shocking murder through all three lead detectives who spent 3 years solving the case. We will explain how a cutting edge school of science was able to extract crucial information from the charred remains of the body. We reveal how a barely readable scrap of paper led detectives to the scene of the murder. And we hear from a woman who was the key to unlocking the case – who has never spoken on television before.

When a Devonshire fisherman hauled in his nets on July 28 1996, he made a gruesome discovery: among that day's catch was a dead body. There was nothing to identify the man's body except a Rolex watch and a small maple leaf tattoo on his hand. After finally identifying the man from the watch serial number, police discovered why he had never been reported missing: the murderer had assumed his victim's identity.

A real life Hollywood thriller unfolded as they pieced together the relationship between the real Robert Platt and his murderer, a man called Albert Walker who had a long history of financial fraud, embezzlement and deception. On the run from Canadian authorities and on Interpol's Most Wanted list for many years, the conman and killer was finally brought to justice by the determined team of Devon & Cornwall detectives.

In 1984 a parcel bomb was sent to a 53 year old grandmother living in a tranquil English village. She died of horrific injuries. No one understood why it had happened. The killer hadn't been near the crime scene, nor even met the victim. The only evidence detectives had was the bomb itself; it was the only link to the killer, but it had been blasted into thousands of pieces. Investigators faced the momentous task of piecing the tiny fragments of bomb back together in the hope that it might give them a shard of critical evidence.

In this episode, we will meet the officers who doggedly fought to bring a bomb-making madman to justice by assembling the evidence into a coherent narrative. We also get moving insight from a family member of the victim who visited the scene shortly after the explosion. And we reveal why it took 18 years to bring the suspect to court.

A 29 year old hairdresser was found brutally stabbed on her doorstep in a quiet suburban street of London. A recording of a threatening phone call seemed to suggest the motive, but every lead comes to a dead end. Her husband, Fadi Nasri made a distraught appeal for help in finding his wife's killer. Both the police and the public sympathised with the man who had lost his wife so brutally.

In an obsessive hunt for critical evidence, detectives finally found the murder weapon after an extraordinary search and refused to give up in the face of daunting odds. Investigators managed to piece together a picture of events surrounding the victim's death from circumstantial evidence, leading them to a shocking conclusion.

In March 1984 Hilda Murrell, a 78-year-old distinguished rose-grower, was found dead in woodland near her home town of Shrewsbury. Despite one of the biggest-ever British police investigations, detectives failed to find her killer and conspiracy theories muddied the waters still further. Police worked quietly and doggedly at their investigation, but it would take a cold case review 19 years later to finally reveal the suspect and tie him to the critical evidence.

This case is a perfect example of how modern technology helped crack a cold case. Through police video and crime scene photographs we piece together the most crucial pieces of evidence. We've filmed with the only detective that was part of the case in 1984 and then carried out the actual arrest of Andrew George in 2003, who had been a 16 year old petty thief when he murdered Hilda Murrell, and thought he had got away with it.

On 12th May 2014 a human torso was discovered in a suitcase during routine maintenance work on a Birmingham canal. With no useable DNA and no other body parts, the case initially seemed impossible to crack. As investigations continued, the police got a breakthrough thanks to an environmental scientist and forensic hydrologist. By analysing flow patterns in the canal, she was able to pinpoint where the suitcase had first entered the water, and where other body parts might be found.

After the identification of the body as Michael Spalding, other important evidence led police to investigate his former landlord. A search of his home prompted a forensic first: the use of 3-D imaging to establish that hidden within a lump of charcoal was a piece of human bone. Simon was convicted and jailed for life in April 2015. This is the first time the case has been featured on television.

In mid-November 1993, Derek Severs and his wife Eileen disappeared without a word. Their neighbours and friends soon became concerned and contacted the police. After a week, police visited the bungalow in which the couple resided, only to find the previously tidy house was now messy, with the kitchen and bathroom carpets removed and a car covered in mud. When police spoke to their son, Roger, he insisted that his parents were simply on holiday. However there was no evidence of this apparent trip, and Roger was soon arrested on suspicion of murder.

They had a suspect – but no bodies and no conclusive proof a murder had taken place. Roger Severs was staying silent, so it was down to the evidence to do the talking.

In the summer of 1993 a serial killer stalked London. The Metropolitan Police investigated a bizarre murder in which a man was found naked on his bed with a dead cat draped over him. He'd been strangled and his flat had been wiped of evidence. It would lead detectives into the secretive world of S&M gay sex and to suspect that this murder was linked to several others. These suspicions were confirmed when they started receiving taunting phone calls from the killer, throwing down the gauntlet to police to catch him.

We will tell the story through the eyes of the Senior Investigating Officers who were there. We hear of the pressures on personal and professional relationships as they move closer to identifying a suspect. And we reveal the key strategy that prompted the suspect himself to provide critical pieces of evidence, finally linking the murders and solving the case. With only the barest of critical evidence to go on, detectives had to play a psychological chess game in the hunt for a multiple murderer.