Gary Allen: Documentary about Yorkshire killer who thought he had got away with two murders airs at weekend

Chasing a Killer: Gary Allen tells the story of investigations by South Yorkshire Police and Humberside Police into a man who murdered two young women 21 years apart.

The documentary, coming to Prime Video in the UK and Ireland, details how detectives linked and solved both cases.

In 2018, Allen killed mother-of-four Alena Grlakova before dumping her body in a stream in Parkgate, Rotherham.

Two decades previously, in 1997, he had murdered Hull woman Samantha Class, 29, and deposited her body in the Humber estuary. Despite going on trial for Samantha's murder a few years later, he was found not guilty and walked free.

The two episodes of the documentary, which will be available to stream from Sunday February 22, chart how SYP's officers teamed up with Humberside Police for a history-making trial in a bid to see justice finally served for both women and their families.

Detectives in South Yorkshire and Humberside applied for the original murder trial verdict to be quashed and were granted permission to charge him with the original murder again as well Alena’s killing.

The investigation into Alena's death was the largest by SYP's Major Crime Unit in several years, consuming a dedicated team for two and a half years and bringing in national and international experts.

Alena was originally from Slovakia and had moved to the UK in 2008, settling in Rotherham with her husband and children.

Her relationship broke down, she lost contact with her children and her lifestyle became more chaotic.

The 38-year-old was last seen alive on Boxing Day in 2018 and was reported missing to SYP on January 15, 2019.

Detective Chief Inspector Mark Oughton, the senior investigating officer in the case, said: “It seems like only yesterday that I got the call to inform me of a high-risk missing person in Rotherham.

“This case was initially a missing person investigation. It was complex; with many unconfirmed sightings reported, concerns about Alena's relationship with others in the Roma Slovak community, and fears of trafficking and exploitation.

“To start off we didn't know if she had tragically taken her own life, been killed, or simply returned to Slovakia."

Then one day, Detective Constable Richard Stump - who also features in the documentary - walked into DCI Oughton's office and played him a series of audio recordings Allen had made on an MP3 player seized during enquiries.

In the chilling recordings, Allen can be heard threatening Alena and losing his temper. This was the tipping point for the investigation to become a murder inquiry, and plans were put in place to arrest Allen for a bodiless homicide.

DCI Oughton recalled: "The day before I planned to arrest Allen, I got a phone call to say her body had been found. It was a bittersweet moment.

“Finding a body obviously greatly assists a murder investigation - but it also confirms to a hopeful family that their loved one will never be coming back alive. Alena's family have steadfastly remained at the forefront of our minds throughout this significant inquiry and in the years since."

At Sheffield Crown Court in 2021, following a nine-week trial, a jury found Allen, then 47, guilty of both murders. He was sentenced to life in prison with a minimum term of 37 years.

DCI Oughton added: "At the time of Alena's death she was making plans to return to Slovakia to make a fresh start and turn her life around. Allen cruelly and violently took this opportunity from her just as she was making plans for a brighter future.

“My heart goes out to her children and loved ones, who will so tragically never have Alena in their own futures.

“I am immensely proud of the work my team and I put into this investigation; it is a case I will remember for the rest of my life. I hope viewers of the documentary will be moved by the stories of Alena and Samantha, and assured by the lengths we will go to pursue justice on behalf of members of our communities who no longer have a voice of their own.”