Two men have been arrested on suspicion of murder after an 85-year-old man was found dead at the side of a road.
The pensioner was pronounced dead at the scene.
The force said four people were arrested hours after the victim was found, including two men, aged 24 and 33, who were detained on suspicion of murder.
A 60-year-old man and a 27-year-old woman were also arrested on suspicion of assisting an offender.
Police said all four suspects remain in custody.
'We do not believe there is any wider risk to public safety'
Detective Inspector Kaz Smithson said: "We have launched an investigation to establish the circumstances surrounding the man’s death, which is currently being treated as murder.
"Our thoughts and sympathies are with those who may have known the victim at this very difficult time.
"We quickly made four arrests in relation to this incident thanks to the swift work by officers but our inquiries remain ongoing.
"I would like to reassure the community that, while we do not believe there is any wider risk to public safety, there will be an increased police presence in the area while we carry out further investigations.
"We are now urging anyone who may have heard something, saw anything suspicious, or has any information to come forward and speak to an officer as any information, no matter how small, may be of a great help to our investigation."
The force would also like to hear from anyone with CCTV or dashcam footage.