The Independent Police Complaints Commission is investigating the contact South Yorkshire Police had with a murder victim before his death.
The watchdog launched an investigation in December last year when detectives investigating the murder of Craig Nelson, who was killed by his ex-partner and her lover, established that threats against Mr Preston had been reported to South Yorkshire Police before his death.
The IPCC is looking at the actions taken by the force over the threats and announced today that there is an 'indication of misconduct by a detective constable'.
The officer concerned has been informed.
Mr Preston, also known as Craig Nelson, was found battered to death near to the Woodhead Tunnels, close to the Woodhead Pass, Derbyshire, in August 2016.
His ex, Leonie Mason, 24 and her partner Shiraz Bashir, 42,were found guilty of murder last month.
Bashir was jailed for 22 years and Mason for 19 years.
Three teenage boys they recruited to help them carry out the killing were found guilty of manslaughter.
An IPCC Spokesman said: "In this case it was important that the IPCC investigation avoided any risk of prejudicing the criminal trial - as such we decided to suspend it for a time.
"Although our investigation is in its early stages, the conduct of an officer at South Yorkshire Police is under investigation, and we are continuing to gather all relevant evidence in this case.”
Mason, Bashir and their teenage accomplices, killed their victim in a lay-by off Town Lane, Rotherham.
Before leaving the lay-by Bashir took a picture of Mr Preston as he was lying bleeding to death in the boot of Mason's car as a 'souvenir'.
The killers threw Mr Preston's body down a ravine close to the Woodhead Tunnels, where it was found by dog walkers the following day.
During the murder trial, it emerged that two weeks prior to the fatal attack, Mason lured her ex a 'quiet spot' in the Rotherham countryside where Bashir attacked him - but he escaped.
It was this 'set-back' that led to the couple recruiting three young boys, two aged 15 and one 14, to help them with their plan.