David Holden, a former member of the Grenadier Guards, was 18 at the time of the killing in 1988.
Former soldier David Holden has been found guilty of the manslaughter of Aidan McAnespie in Tyrone 34 years ago.
The 53-year-old is the first veteran to be convicted of a historical offence in Northern Ireland since the 1998 Good Friday Agreement.
Mr McAnespie was killed by a shot which ricocheted off the road and struck him in the back.
He was walking through a border crossing on his way to a Gaelic football match
The judge found that Holden had pointed a machine gun at Mr McAnespie and pulled the trigger, while assuming the gun was not cocked.
The judge said: “That assumption should not have been made.”
He also told the court that Holden had given a “deliberately false account” of what happened.
The judge dismissed the defendant’s claim that his hands had been wet from cleaning duties.
The court heard Mr McAnespie was unarmed.
A further hearing to determine the sentence will be held in the new year.
Holden, who was serving in the Grenadier Guards and was aged 18 at the time, was on his first day of checkpoint duties.
Mr McAnespie was known to security forces as a “person of interest” – an IRA suspect.
Holden was initially charged with killing Mr McAnespie in September 1998.
At that time, staff from the Director of Public Prosecutions met with the senior RUC investigating detective and a forensic firearms expert and decided to withdraw the manslaughter charge.
In December 1988, Holden was subsequently charged by the Army under Section 69 of the Army Act 1955 with the offence of “prejudice to good order and military discipline” and was fined £370.86 by his commanding officer.
During the trial, defence counsel Frank O’Donoghue KC told Mr Justice O’Hara: “My client, by the age of 19, believed that this matter was behind him and he could pursue his own life and left military life in 1990.”
The court heard that in 2008, the PSNI’s Historical Enquiries Team (HET), reviewed the case of Mr McAnespie and produced a report for his family.
Seven years later, the Attorney General for Northern Ireland invited the director of the Public Prosecution Service (PPS) to review the case in light of the HET report.
In January 2018, the PPS informed Holden that a decision had been taken to prosecute him for Mr McAnespie’s manslaughter.