David Brickwood, 74, was stabbed five times in Northampton on 26 September in a "violent and dreadful" attack.
One of his sons, Dale Brickwood, said the family was becoming "increasingly frustrated" the killers had not yet been brought to justice.
Police said the case was "a priority" they were "committed" to solving.
Mr Brickwood was attacked when several men broke into his Lindsay Avenue home in the early hours of the morning.
He was left with multiple stab wounds to the head, leg and hand.
The scrap metal dealer was known to keep money in his house.
His son Dale said the family was not sure how much was taken but during a Crimewatch reconstruction on 8 February police appealed for "anyone [who has] come into contact with a large amount of old style £20 and £50 notes" to come forward.
His son said watches and jewellery were also taken.
The offenders would have been "covered in blood", officers said, but despite that, no-one has been charged.
Two men arrested shortly after the murder were released with no further action. Three other men remain on bail.
Mr Brickwood criticised Northamptonshire Police for a lack of communication, saying: "We seem to be finding information and giving it to them."
The police "don't really talk to us", he added.
Northamptonshire Police said two family liaison officers had been assigned plus a "dedicated team of detectives".
Det Ch Insp Mick Graham, leading the investigation, said: "I can fully understand that the family and friends of David may be frustrated.
"The investigation team share that frustration and empathise with David's family."
He said there was "a lot of rumour and speculation locally",  but added: "We need the people with the critical pieces of information and evidence to come forward."
However, the family has been left "so demoralised" after the recent Crimewatch appeal failed to lead to further arrests, Dale Brickwood said.
"It's disgusting. Five months after our dad was murdered and no-one's been caught. Where do we go from here?"
Crimestoppers has offered a £10,000 reward for information leading to the arrest and conviction of those responsible.

Hassan al-Mandlawi, 32, and Al-Amin Sultan, 30, both Swedish nationals, were found guilty of actively taking part in the murders, which were filmed.
The Gothenburg court convicted the pair even though they did not wield the knife used in the killings in Aleppo.
The men had denied the charges and will appeal the verdict, their lawyers said.
The court in Gothenburg, south-west Sweden, was presented with footage of the murders that was discovered on a USB stick in Sultan's home.
Two men are heard giving directions in Swedish. One prisoner is beheaded, the other has his throat cut.
The court found the duo had actively taken part in the murders, though they did not hold the knife.
It also ruled it had been proven that the pair fought in Syria during the spring of 2013.
Anti-terror campaigners have applauded the verdict, pointing out that it shows that Sweden is prepared to put people on trial for crimes committed in other countries.
The case against the pair is the first time that a "terror crime" - as opposed to "crimes against international law" have been staged by a Swedish court, Radio Sweden reported.
In order to secure a conviction for a "terror crime", the prosecution must prove that the intention was to cause fear among others.
A crime against international law is defined as a case where it has been proven that the men fought with a group in an armed conflict.
Sultan's lawyer insisted that it was not his client's voice in the film and accused the prosecution of singling him out because he was wearing similar clothing to the guilty person, Radio Sweden reported.
The defence argued that pictures of him posing with weapons were taken when he was in Turkey and Syria doing volunteer relief work.
His accomplice, Mandlawi, uses a wheelchair after being shot while allegedly working abroad as a sniper and has suffered brain damage, Radio Sweden quoted his lawyer as saying.
Mandlawi's defence team said that the evidence against him was meagre.
More than 250,000 people have died in nearly five years of civil war in Syria.
The son of a man murdered at home five months ago has said his family is "demoralised" by the apparent lack of progress in the investigation.
[NEXT_CONCEPT]
A court in Sweden has sentenced two men to life imprisonment over "terror crime" murders carried out by Islamic State militants in Syria in 2013.