True story behind ITV's Delia Balmer and what happened to killer John Sweeney

's latest drama, Until I Kill You, plunges viewers into the terrifying true story of agency nurse Delia Balmer (Anna Maxwell-Martin) from London.

Delia thought she found a soulmate in John Sweeney (Shaun Evans), a carpenter and apparent kindred spirit. The story unfolds following their meeting at a Camden pub in 1991.

On the surface, it appeared Delia had struck romantic gold with Liverpool-born Sweeney, who seemed to be an attentive partner, showering her with flowers and affection. However, as the series and her harrowing experiences reveal, beneath the facade was a man capable of unfathomable violence.

Drawing on Delia's chilling memoir, 'Living With a Serial Killer', published in 2017, she looks back at those days with regret for not seeing the warning signs, writing: "Subtle changes happened slowly. I should've known something was wrong but I am too soft and trusting. I'd never come across anything like it before."

The show captures the spiral of terror as Sweeney moved into Delia's home, revealing his volatile anger, before taking control in a manner that was both abusive and frightening, leading to years of living in constant fear.

It wasn't until much later that Delia mustered the strength to confront him and demand he leave - a decision met with a horrific response. Despite Delia's initial request for him to leave, Sweeney's manipulation of her intensified, leading to a harrowing period in the spring of 1994 when he held her captive.

During this time, he restrained her to a bed and threatened to cut out her tongue if she screamed. While holding Delia hostage, Sweeney admitted to the murder of his former partner, Melissa Halstead, whose dismembered body was found in a Rotterdam canal in 1990.

Delia recounts his haunting admission in her book: "We had a room in Amsterdam. I went in. There were two Germans there with her. I killed them all. I didn't know what to do with the bodies. I sat with them for three days. On the third day, I cut them up, and I put them in bags and I threw them in the canal."

Delia, fearing for her very life, tread carefully to avoid provoking Sweeney, who eventually released her. She later reflected on the ordeal, stating: "He was very quick, and if I had tried anything, I probably would have ended up cut up."

Tragically, Delia's suffering at Sweeney's hands did not end with her release; he continued to pursue and attack her, culminating in a brutal axe assault that left her with serious injuries.

Sweeney cunningly eluded the grasp of the police for years, until ultimately his heinous actions caught up with him when he later murdered Paula Fields in 2000, reports .

Her remains were discarded in Regent's Canal, London. In 2001, Sweeney was arrested and slapped with a nine-year term for his assault on Delia. While Sweeney languished in Gartree Prison in Leicestershire for the assault, the detectives probed further connections to Melissa and Paula.

Breakthroughs in DNA evidence, alongside first-hand accounts from Delia, allowed the law to catch up with the monstrous Sweeney, ensuring he was put in prison for good.

After a guilty verdict for the murder of both victims, Sweeney received a whole life sentence in 2011 and is currently behind bars, with no hope for release. It has also been chillingly noted that Sweeney may have snatched away the lives of three more women, unaccounted for between 1970 and 1990.

The convicted murderer disdainfully remained in his cell at Belmarsh prison as his fate was sealed by Mr Justice Saunders who remarked: "These were terrible, wicked crimes. The heads of the victims having been removed, it is impossible to be certain how they were killed. The mutilation of the bodies is a serious aggravating feature of the murders."

Delia, who was closely involved in the production of Until I Kill You, reflected on her experience working alongside writer Nick Stevens as they molded the draft script.

Speaking candidly to ITV prior to series airing, Delia confided: "When I wrote my original story, I included every detail of what happened. When it came to the final attack on the doorstep, I edited it over and over again, wanting everything to read precisely as it had happened."

Explaining the importance of sharing her truth, she continued: "My concern has always been to get the truth out by whatever means. I remain an angry person. Sweeney was let out on bail. The police gave me insufficient protection before his final assault. Later, I was forced to go to court to be further traumatised by the system."

Delia has courageously rebuilt her life following the harrowing events, yet she admits that the trauma endures, impacting her mental health years later.

She said: "I often suffer from depression and anxiety, afraid of life and afraid of the future, a compulsive worrier. When I look in the mirror I see a stranger. Certain physical pain, I will have for life. I am stuck. I cannot move on, and cannot go further.

"Fear holds me back from doing certain things. I live for travel, but it is has also become almost my only escape from reality. Ballet classes have always been an important part of my life."