STABBED 22 times and left to decompose in bleached water, the so-called ‘Angel of Mercy’ spared his vulnerable victims no dignity - even after their deaths. The serial killer, later unmasked as Andrew Dawson, 47, butchered two elderly men he befriended in a Derbyshire block of flats in “very violent and vicious” attacks, back in 2010. Inspired by sawn-off shotgun murderer Raoul Moat, who led police on a six-day manhunt just weeks earlier, he then went on the run armed with a "killing kit" of knives, camping equipment and a fishing rod.

Dawson was apprehended within days and it was arrogance that led police to him through a series of clues - including a rose left on his first victim’s pillow, bloodied water residue and the imprint of a twisted letter to police on a notepad in his flat. In the missive, which was never sent, he dubbed himself "(TH)e Angel (OF) MERCY", labelled the flower "a nice touch" and revealed he had killed but would only reveal the address if the body wasn't found within a week.

The crimes of Dawson, who was handed a whole life order in 2011, are being reanalysed in True Crime Presents: Tracking A Serial Killer on ITV tomorrow, which reveals how his troubled childhood sniffing glue at 13 progressed to mass murder. There were multiple warning signs about the ‘Angel of Mercy’ before his “very violent and vicious” second killing spree and he had been recalled to prison three times after being released on licence in 1999.

His first murder occurred in 1981 when he was 18 years old. Dawson broke into a hardware shop owned by Henry Walsh, 91, in Lancashire, tied him up, stabbed him a dozen times with a bread knife and stole his pension book. Dawson had been raised in a “poor but not impoverished home” and was regularly in trouble with the law from the age of 13 when he started sniffing glue. Later he progressed onto cannabis and other drugs.

His brother Malcolm “wasn’t surprised” by the 2010 attacks noting his sibling, one of six, had “always been a violent man”, adding: “He was an evil psychopath and it was only a matter of time before he killed again.”. Even in prison, Dawson was “no shrinking violet”, allegedly branding serial killers Peter Sutcliffe, known as ‘The Yorkshire Ripper’, and Dennis Nilson, a necrophiliac, “wimps” and claiming to be “a better man”.

But in 2010, 11 years after his release on licence, the 47-year-old moved to a block of council flats for “single, vulnerable men”, on on Waterford Drive, following the breakdown of the relationship with the mum of his two kids. Two weeks after moving there, Dawson killed kitchen porter John David Matthews, 66, known as ‘Grandad’ to colleagues, after the elderly man allowed him to use his washing machine.

He stabbed him 18 times before astonishingly taking his children on a day out. The next day Dawson cleaned the flat “to destroy evidence” and put the body in a bathtub filled with bleach - but not before an unusual act. Senior Investigating Officer (SIO) Paul Callum explained he “redressed him” and “we believed he lay down on the bed in Mr Matthews' flat and put a rose next to him”. It took days for John’s body to be found. Authorities were only alerted when he didn’t show up for work and they forced entry after spotting flies by his window.

At the flats, police bumped into a dishevelled man, who claimed not to know where his neighbour John was, returned to his flat and quickly left the scene. Unknown to them, it was Dawson. Cops were unaware they were looking at a murder at that point due to the victim’s body having swelled up so much in the water, masking knife wounds. Shockingly, there was another twist. This is no hoax if you don’t find him in a week I will give you his address. The pink rose was a nice touch. Yours (TH)e Angel (OF) MERCY.

SIO Callum said: “When the officers attended on the Sunday to find Mr Matthews, we think that Dawson was upstairs murdering or having just murdered Paul Hancock.”. This would explain the frantic nature of his quick departure from the flats and the mass of evidence at the second crime scene, found days later in what was said to be a “sinister discovery”. Unlike the first, where it was clear efforts were made to destroy evidence, it was as if “the cleaning up of the flat has been abandoned midway through”.

Paul Hancock, 58, was found in a bathtub “full of sludgy water”, bleach, discarded clothes, inside-out marigolds and the tip of a broken knife. SIO Callum said this crime scene was “very rushed, untidy and with lots of blood spatter over the lounge”, unlike the home of first victim John, which was “ridiculously clean”. It would ultimately lead to Dawson’s conviction. Meanwhile, the killer had gone on the run. Police tracked his 200-mile journey north from Derby to White Haven, Cumbria, through his card payments, train tickets and CCTV from train stations.