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Known as the 'Angel of Death,' Beverley's story is one that will chill you to the bone.
The nurse, then aged just 21, killed four children in cold blood while working at Granthan Hospital, and went on to laugh about it in court, and shrug off all accusations during police interviews.
The deaths of seven-year-old Liam Taylor, 11-year-old Timothy Hardwick, two-month-old Becky Phillips and 15-month-old Claire Peck all happened within 59 days in 1991, after Allitt tampered with their injections before other hospital staff suspected anything, and dosed them up with fatal doses of insulin.
Now, new Quest Red documentary British Police: Our Toughest Cases seeks to shine light on Beverley's scheming and the poor children she killed by speaking to the investigators that caught her and even a parent of one of the victims.
Looking back on the horrific crimes, we learn that Allitt was so unphased when she was charged with four counts of murder that she let out a laugh.
DSI Stuart Clifton, who interviewed her, recalls: "She's placed in a police cell, and you have to remember that this is a girl that's about 21 years of age, never been in trouble with the police, she gets all of these charges and she's laughing. She's happy about them.
"She was an evil, callous, calculating person. She knew what she was doing. These are defenceless children who rely on her and she's attacking them."
Grantham Hospital's Children's ward had suffered four infant deaths and the highest number of collapses in children the hospital had ever seen, but at first nobody ever suspected Allitt of being responsible.
She covered her tracks, ripping papers out of hospital log books, and at first it worked.
Eight-week-old Liam was suspected of having died of a heart condition, while the rest of the deaths were similarly brushed off as health blips. All the while Allitt was busy gaining the trust of the children's parents, even being asked to be a godmother to one of them.
However, eventually one concerned staff member called the police - and when the attention turned to staff on the ward and Allitt was called in for questioning, her interviewer Detective Michelle Billingsley instantly found her "evasive".
"She tried to bamboozle us," Michelle says in the doc. "We were trying our best to talk about the insulin and the affects it had on the body, but we weren't medically trained, and I think she could easily pick up on this."
In the tapes, played on film for the first time, Allitt is asked why she killed five-month-old Paul Crampton, to which she replies: "I'm really going to give a harmful drug to a helpless baby?"
Meanwhile, we also hear how she tried to pin the blame on others before she was finally charged with the four murders, as well as 11 attempted murders and 11 counts of causing grievous bodily harm.
You'll have to watch the documentary to hear how dismissive she is in the interviews, but it really is chilling given that we now know she's responsible.
By the time of her trial in 1993, Allitt still appeared to lack remorse, and still refused to plead guilty in court. Despite this, she was found guilty on every charge and given 13 life sentences.
Former Detective Michelle Billingsley, who took Allitt to her first court appearance, says: "I was shocked that someone could do all these things and not feel any remorse whatsoever.
"But not only was there no remorse, it was the smile, the shrugging of the shoulders, she was leaning forward looking out the van at the people that had gathered round the court as if she was looking forward to appearing there."
Following the verdict, the former Home Secretary Michael Howard was given the choice over whether she should be sent to jail or detained instead, and subsequently she has now spent almost 27 years in Rampton Hospital, Notts.
To this day, Allitt still maintains she isn't responsible for all 13 charges, and says that only nine of them were down to her.
This documentary sounds both heartbreaking and fascinating in equal measure.
British Police: Our Toughest Cases airs Saturdays at 10pm on Quest Red.
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