Keiryn Nisbet, 22, was convicted of murdering Ronnie Simpson, 67, at the High Court in Edinburgh yesterday.
The court heard Nisbet entered the flat in Armadale, West Lothian, on 5 October, 2012, and repeatedly punched, kicked and stamped on his victim’s head and body.
The accused had been drinking at the Blether Inn, in the town that day, then had been ejected for being too drunk and allegedly assaulting a barmaid.
The next day, he sent a message to a friend saying he “knocked f*** out of a boy last night” but “canny mind a thing”.
Nisbet denied murder, but forensic experts said the likelihood that blood found on a bedroom wall did not belong to him was one in a billion, and he was convicted by a jury.
Police said they still did not know why Mr Simpson had been attacked.
After the verdict, Detective Chief Inspector Robert Cowper said: “While nothing can undo the pain and suffering Mr Simpson’s loss has had on his family and the impact on the local community, I hope that today’s verdict can allow the family to move forward from this ordeal.
“Mr Simpson was well-known locally and the attack within his own home was a callous act which Keiryn Nisbet has never offered any explanation for.”
Police were called by a neighbour who said he heard “an old man squealing” inside Mr Simpson’s home.
Allan Wilson, 25, told the court he called 999 after hearing an argument and what he drescribed as the sound of a “wardrobe being dropped”.
A recording of the call was played to the jury, in which Mr Wilson told the operator that he could hear “banging doors” and “smashing every two minutes”.
He told the court that there was a “scuffle in the living room which went right through to the bedroom”.
Police were called and forensic scientists found blood from Nisbet on the bedroom wall of his victim’s house.
The court heard how police obtained a blood sample at Mr Simpson’s home and found a full DNA profile which matched that of Nisbet.
Alexander Meechan, 24, told the court that Nisbet wrote a message to him following the attack, in which he admitted attacking someone but could not remember who.
Prosecutors said Nisbet attempted to avoid detection by washing clothing and a pair of trainers that he wore during the attack.
After the verdict, Mr Simpson’s relatives shouted: “Yes.”
Advocate depute Ashley Edwards told the court Nisbet had a string of previous convictions, including for violence in 2009.
He had also spent time in prison, the court heard.
Defence solicitor advocate John Keenan asked temporary judge Norman Ritchie to defer sentence so the court could obtain character reports.
Nisbet will be sentenced at the High Court in Glasgow next month.