Michael McKeown was just 18 when he struck James Ross on February 14, 2022.
The 27-year-old victim – nicknamed Chuckie – never survived the attack at Abronhill Shopping Centre in Cumbernauld, North Lanarkshire.
McKeown – now aged 20 – had faced a murder accusation at a trial at the High Court in Glasgow.
He had claimed to be acting in self-defence.
But jurors today convicted him of the reduced charge of culpable homicide.
First offender McKeown, of Bonnybridge, Stirlingshire, had been on bail during the trial.
However, he was remanded in custody by judge Lady Drummond pending sentencing next month.
The attack occurred around 4pm at the shopping centre while McKeown was out with friends.
CCTV captured Mr Ross – who barely knew the killer – approach the group with an associate.
The court heard McKeown ended up kicking Mr Ross while he also had a knife in his hand.
In his speech to jurors, prosecutor Greg Farrell said the killer then “appeared to lunge forward with an outstretched arm”.
Mr Ross was stabbed in the face and chest.
The victim initially gave chase as McKeown and his friends ran off.
But, Mr Farrell told the court: “Shortly afterwards he would collapse and die.
“This was a brutal assault in broad daylight and McKeown was not acting in self-defence.”
READ NEXT: Uber driver asked his passenger to get out and killed him in hit-and-run
In his evidence, McKeown told his KC Thomas Ross he could not “give a good answer” as to why he stabbed his victim.
He claimed to have a blade as he was a young boy and not from that area.
McKeown insisted to Mr Farrell, in cross-examination, that he had not been “thinking” about knifing Mr Ross.
He claimed it was he who was “fighting for his life”.
Mr Farrell said: “You were trying to show your friends who the big man was here?”
McKeown replied: “I was trying to protect them.”
After the verdict, Mr Farrell told Lady Drummond there were three impact statements completed by relatives of Mr Ross.
St Enoch Centre in the city centre will reduce its parking charges between 5pm and closing, seven days a week. From Friday, May 3, shoppers will
Given he has witnessed some of Britain's most incredible kitchens, you might have thought Kevin McCloud would go for something extra impressive in his own home.
1 Cambrook Court, High Street, Chipping Campden GL55, @the_dresser_cotswolds Ava & Iva ‘Off the beaten track, but well worth discovering. Ex
"I dedicated my whole life to Clarks," Ms Carnick said. (Representative pic)An 82-year-old woman in the UK who worked at Clarks for nearly seven decades has bee