• Keith Johnston is now an ordained Baptist minister and preaches regularly in Dalkeith
Reverend Keith Johnston said he turned to Christianity while in jail for the stabbing of classmate Steven Hughes during a fight outside his victim's grandmother's house when he was 16.
Despite standing trial for murder and facing calls at the time from his victim's parents for him to be jailed for life, Mr Johnston was found guilty of the lesser crime of culpable homicide and spent five years in prison for the killing.
Now aged 36 and the minister of Dalkeith Baptist Church in Midlothian, Mr Johnston said: "As a youth, foolishly, I had always thought that, if you did something like I did, then you'd wear it proudly, that you'd think 'bring on another one'.
"But once in my prison cell it dawned on me what I had done and it cut me to the core. I was bowled over with anguish and grief."
It was while in prison, Mr Johnston said, that speakers from the Christian Prison Ministries "spoke right to my heart".
Following his release, he studied divinity and trained as a minister.
He said: "Through my faith, I now know my life doesn't have to be a waste. I'm trying to bring a sense of good to society.
• Seeing the light through a prison cell window
"And I'm trying to do as much as I can in memory of Steven, the lad I killed."
While most of Mr Johnston's congregation are aware of his past, he said that he had decided to speak publically about it as he believed it could help other young people who found themselves involved in violence.
Jeremy Shaw, senior pastor at Dalkeith Baptist Church, said the congregation was fully supportive of Rev Johnston.
"Keith has been transparent all the way along with us about his past, and most people here know his story," he said.
"Some in our congregation may be more comfortable than others about his background... I believe he is an inspiration to many people."
Mr Johnston said the boy he killed in Bonnyrigg in 1990 had once been a good friend but they had later fallen out.
Described by his grandmother, as "an obliging boy who would have done anything for you", Hibs fan Steven had been friends with Mr Johnston since primary school and had just started his first job since leaving Lasswade High School, as a trainee chef in Dalkeith.
Mr Johnston recalled how he went to Steven's grandmother's house with a kitchen knife to frighten and humiliate him.A fight broke out and, as they swapped blows, he stabbed him through the heart.
Mr Johnston said that he had thought of attempting to evade the police by fleeing to England and changing his name, but at least six other youths had witnessed the stabbing and he was met by police when he returned to his parents' home.
During the three-day trial in 1990, the judge, Lord MacLean, described the incident as a tragedy for both families but said Mr Johnston had taken the life of someone who was his close friend.
"That life was taken away needlessly and of course it will be with you for the rest of your life," he said.
Mr Johnston was convicted by a majority verdict of culpable homicide and sentenced to seven years in prison, a sentence the dead boy's mother June Deans and his step father Geoff Deans condemned at the time.
Mrs Deans said at the time: "We were looking for a life sentence because our son killed in cold blood.
"If you rob a bank but don't hurt anyone you could easily get 10 years."
She described the sentence as "just not good enough", adding: "They call it justice but our son is dead and the boy that killed him could be out of jail by his 21st birthday."
Mrs Deans was not available for comment last night.
Mr Johnston was due to address his congregation at the church last night.