The victim, in his 30s, was declared dead at the scene in Calcutt, near Cricklade, shortly after 8.15am on Sunday.
A man in his 70s and a woman in her 40s have been detained on suspicion of firearm possession and assisting an offender as part of the murder enquiry. Both have been placed in custody, a cordon has been established at the location, and the road approaching the site has been closed.
Police appeal for witnesses
Detective Chief Inspector Phil Walker said: "This is an incredibly serious incident, and my thoughts are with the victim's friends and family at this devastating time.
"Enquiries are ongoing at the site and in the wider area to establish the circumstances which have led to this incident and locate all the people involved.
"A cordon is in place at the site and the road leading to it has been closed to allow for enquiries to be conducted and I would ask that this is respected.
"Those in the area will see an increased policing presence throughout the evening as enquiries continue. We are really keen to hear from anybody who has any information or witnessed anything suspicious this morning."
