A couple shot dead in their seaside bungalow had called police to report a prowler just hours before their bodies were found, detectives have revealed.
The Stirlands had lived in the town for about six months
The bodies of John and Joan Stirland, 55 and 53, were discovered at their home in Trusthorpe, Lincs, on Sunday.
Mrs Stirland's son, Michael O'Brien, is serving life for the murder of a man outside a Nottingham pub.
Police say it is possible the couple were murdered in revenge for her son's killing of Marvyn Bradshaw in 2003.
Mrs Stirland spoke to a Nottinghamshire police officer at around 1400 BST on Sunday to report a suspicious person in the area, a Lincolnshire Police spokesman said.
Half an hour later, a car, which is believed to have been used by the killers, was discovered burning around two miles away in Hannah cum Hagnaby.
A police spokesman said: "Mrs Stirland spoke to an officer in Nottinghamshire just before 2pm on Sunday, saying that her neighbour had seen a man hanging around the house the previous evening.
"This had not been reported to Lincolnshire police and she emphasised that she did not want the background of her and her husband revealed and asked for a normal response to a prowler incident.
"The car, which we believe was used by the killers to leave the scene, was found burning at 2.30pm two miles away.
"Therefore, we believe the Stirlands were killed between 2 and 2.30pm on Sunday."
The bodies were discovered by police in the bungalow on the Radio St Peter's estate at around 2130 BST on Sunday.
Police have also appealed for more information on a dark Volkswagen Passat found burning two miles from the murder scene.
At a news conference on Tuesday Det Supt Graham White confirmed the couple died from gunshot wounds but would not say how many shots were fired or what sort of gun was used.