Channel 5’s documentary Sadie Hartley: The Clues That Caught The Killer looks at how, why and by who Sadie was murdered.
Who murdered her and what happened during the attack feature in the one-off documentary tonight.
The lead-up to the murder
Sadie’s husband, Ian Johnston, was once in a relationship with a woman called Sarah Williams.
But he ended it after she became “possessive and difficult”, jurors later heard at the trial.
However, Williams wanted to rekindle her relationship with Ian and, according to prosecutor John McDermott QC, she had accomplice Katrina Walsh on hand to help in the plot to get her ex back.
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In 2014 – at which point, Ian and Sadie had been together for nine years – Williams sent Sadie a later claiming she had had an affair with Ian behind Sadie’s back. Her plan was to split them up.
In the note, she claimed to have had “unbelievably fantastic sex” in the affair and wrote: “We’ve never been able to get enough of each other.”
It didn’t work, though, and Ian and Sadie remained together.
In December 2015, Williams and Walsh went to Germany and bought a cattle prod.
A week before the murder, in January 2016, Walsh dropped flowers off at Sadie’s home in Helmshore, Lancashire as a test run for their horrific plan.
What happened during the attack on Sadie Hartley?
A court heard how Williams used the cattle prod to stun Sadie.
While she was down, Williams proceeded to stab her victim 41 times in what was described in court as an “orgy of violence”.
Mr Justice Turner, during the sentencing at Preston Crown Court, said Williams “slaughtered [Sadie] like an animal” and likened the method to a “clinical assassination”.
Officers were able to use a number of pieces of evidence to put together an accurate picture of what happened.
How did police find Sadie Hartley’s killers?
Cops found Sadie’s DNA on Williams’ bath and a pair of the killer’s glasses had a minute trace of blood on one of the lenses.
They also found the stun gun and matched it to injuries on Sadie’s cheek.
Elsewhere, police discovered that Walsh had gone into a Tesco store and bought a carving knife that Williams used in the attack.
Among the most incriminating pieces of evidence, though, were Walsh’s diaries. She kept detailed reports of her meetings with Williams.
Let no one believe this was a crime of passion. This was a crime of obsession.
The diaries showed they had planned the killing for more than 18 months before carrying it out.
Mr Justice Turner, when sentencing, said it wasn’t a “crime of passion”.
He told the court, as reported by the BBC: “Let no one believe this was a crime of passion. This was a crime of obsession, arrogance, barbarity and pure evil.”
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Both Williams and Walsh received life sentences for what they did to Sadie.
The judge ordered Williams to serve a minimum of 30 years behind bars.
Walsh, meanwhile, was ordered to serve at least 25 years because she “planned and rehearsed [the crime] down to the finest detail”, including helping to hide evidence.
What is the Sadie Hartley documentary and when did it air?
Sadie Hartley: The Clues That Caught The Killer, first aired in 2019 on Channel 5.
The other episodes in the series cover two other well-known murders.
These are the murder of Rhys Jones and the killings carried out by Fred and Rose West.
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