The BBC's Crimewatch programme has featured a reconstruction of the murder of a pensioner who was tied up and battered to death.
Barry Rubery, 68, was found dead at his cottage in Latteridge Road, Iron Acton.
Police believe he was murdered during a botched burglary, but despite a £10,000 reward they still have no firm leads.
They want information about a dark Land Rover Defender seen outside the property on 28 April, the day before Mr Rubery's body was discovered.
His son, Philip, 48, told a news conference: "I know the police and forensics are really giving it 110% and we are grateful, but they do need that little bit of help from the public."
His daughter Julie, 45, said: "Somebody must know something."
Police know Mr Rubery, a former farm worker, returned to his home at 2245 BST on 28 April after spending the evening with friends.
He was found dead at 0800 BST the next morning. He had been bound with electrical cable.
A post-mortem examination revealed the cause of death to be head injuries from a "significant and sustained" physical assault.
Police say Mr Rubery was a "fit, strong and healthy" man with a boxing background, who would have put up a "solid defence" to any attack.
Det Ch Insp Garry Reeves, who is leading the investigation, said: "We know that Latteridge Road is a very, very busy road at all times of day and night.
"Witnesses have spoken about a dark Land Rover Defender - which is a twin-cabbed vehicle, with a long wheelbase and either a hard or canvas covering at the back.
"People have told us that a vehicle such as that was parked outside the cottage at 10.30pm [on 28 April]."
Crimewatch, BBC1, 2100 BST on Tuesday 15 June