Police forces to check old unsolved cases after Gary Allen found guilty of two murders 20 years apart

Allen was found guilty of killing Samantha Class in Hull in 1997 and Alena Grlakova in Rotherham in 2018 and also has convictions for violent attacks on two other women in Plymouth in 2000.

The catalogue of offending against women has raised questions over whether the 47-year-old might have been responsible for further violence.

Although Allen spent the best part of a decade in prison following the Plymouth attacks, he was free until he was arrested over Ms Grlakova’s disappearance in 2019 and was known to have moved around the UK.

Detective Chief Inspector Mark Oughton, who led the investigation into Ms Grlakova’s killing for South Yorkshire Police, told the PA news agency: “This is a concern for us too.

“We’ve mapped Gary Allen’s movements when he’s been at liberty throughout that period and we’ve worked closely with the National Crime Agency’s analytical section to find out what other offences were in those areas at that time.

“What we’re now going to do is to write to individual forces to make them aware that Gary Allen was in the area at that time and ask them to review any crimes that were in that area at that time.”

Mr Oughton said: “I think Gary Allen’s a very dangerous individual and I I think he would have gone on to attack other people if he had not been convicted today.”

The senior detective said South Yorkshire Police’s investigation into the death of Ms Grlakova is one of its largest for many years.

Mr Oughton said the inquiry began as an investigation into Ms Grlakova’s disappearance, which was reported in early January 2019.

And he said his team recovered 37,000 hours of footage and investigated 125 sightings.

He said he became extremely concerned when its became clear Ms Grlakova had had “significant contact” with Allen.

Ms Grlakova’s body was found in a Rotherham stream that April – four months after she went missing – and questions have been raised about why it took police so long to find the body.

Mr Oughton said the area had been searched but not the watercourse and it was very well concealed in the stream bed.

He said: “I fully appreciate there would have been concerns among the public.

“I just want to stress the complexity of the investigation.

“This was not a murder investigation until April, 125 sightings had to be investigated, we had to look at CCTV of those sightings, house-to-house, visit witnesses, etc.

“There was obviously a massive area to be searched around those sightings so that area that was searched was one of many that had been searched.

“And it was only following the declaration of a murder inquiry and Gary Allen as a suspect that we started to refocus and found that the stream in Parkgate needed to be searched.

“It was as part of that review that South Yorkshire Police unfortunately found Alena. She had been very well concealed in the stream bed.”

The detective said: “Alena was a mother with four children, she was a daughter, she was a sister.

“She was wanting to go back to Slovakia and to start her life and get back to the person she was.

“Unfortunately, that night she was vulnerable. She went to Gary Allen’s address and that’s the night I believe he murdered her.”

Mr Oughton said: “I welcome the conviction today of Gary Allen but my thoughts, the thoughts of South Yorkshire Police and Humberside Police are with the two families.

“Alena’s family have had to wait two-and-a-half years for justice. Samantha Class’s family have had to over two decades.”