Kevin James Pettiford admitted to the murder in a chilling confession to police, but he later pleaded not guilty on the grounds of mental impairment.
On Wednesday, a jury determined the defence could not be upheld, finding the 38-year-old guilty of one count of murder and another count of attempted murder over a separate incident.
Pettiford said he went back and forth in his mind over whether he should kill 56-year-old Andrew Murray, who was sleeping rough in Tweed Heads, in far-north NSW, in November 2019.
Video of his confession was played during his murder trial in the NSW Supreme Court last month, showing him explaining that his victim was simply in the wrong place at the wrong time.
"I just can't lie ... it was me," Pettiford told investigators.
"(I) bashed his head in."
Immediately following the confession, Pettiford, who was also homeless at the time, was arrested for murder, to which he replied, "That's fine. All good."
He said from a young age he had the impulse to kill, which got worse as he got older.
"All I know is I've always just wanted to f***ing kill someone," he said.
Pettiford said he struck Mr Murray five or six times in the temple with three large rocks and after the first blow he knew his victim was likely brain dead.
"I hit him the first time, straight away I knew he was f***ed," he said.
"I did it a couple more times with another rock."
Pettiford described himself as "emotionless" during the attack, but he said he didn't intend for his victim to suffer.
"He was at the wrong place at the wrong time. That was it."
Pettiford said that before the murder he hesitated multiple times before something inside him just went "go".
He also told investigators that roughly a decade earlier, while undergoing a court-ordered rehabilitation program, he admitted to having wanted to follow and kill two people one night when he was drunk.
"I told them something very disturbing and they did nothing about it," he said.
"I should have been f***ing locked up in the looney bin."
Pettiford said on another occasion, when he was about six or seven, he threatened two children with a knife and told them, "you're going to f***ing die."
"From that point I was like 'f*** there's something wrong with me'," he said.
A sentencing hearing has been set for February next year.
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