Christopher Wayne Patterson (50) was jailed for life in 2008 for the murder of 18-year-old Michael Hutchings, who was dumped in the Clutha River by Patterson, with the help of his partner Nichole Field.
Patterson appeared before the Parole Board for the first time last month, when he was denied early release.
At the hearing, before board chairman Ron Young, the prisoner spoke for the first time about why he killed Mr Hutchings.
The victim, Patterson said, had been involved in a car accident in which a young boy was hurt.
The father of the boy was apparently a gang member and Patterson said he became concerned Mr Hutchings would be killed in retribution.
Patterson said he encouraged the teenager to flee to Australia but it did not work out and he returned to live with the defendant and his partner at their home in Kaitangata.
Patterson told the board Field convinced him that either Mr Hutchings was to be killed for causing the injury to the boy or he would be killed instead.
It was a case of "him or me", the killer claimed.
The alleged background, Sir Ron said, was "somewhat unusual" and in discussions with a psychologist, Patterson too, accepted the apparent strangeness of the circumstances as he presented them.
Mr Hutchings was murdered on the evening of January 7, 2008, after a stab wound in his right side pierced his abdomen and passed through his liver, causing fatal bleeding.
At sentencing the court heard there was a less serious wound to the victim’s neck and an injury to his hand which indicated a struggle had taken place.
The body was wrapped in a mattress protector, left in the house for almost 24 hours and then moved to the Clutha River, where it was weighted with two metal bars, each weighing 51kg, and rolled into the water.
Field, a former nurse aide, admitted a charge of being an accessory and was jailed for two years.
The couple were jointly charged with the rape of a young girl which was alleged to have happened at their Kaitangata home a couple of weeks before the murder, but the charges were later dropped.
There was some suggestion Mr Hutchings had been a witness to the alleged incident but that was never established.
The Parole Board, at last month’s hearing, was told Patterson had recently begun a nine-month rehabilitation course, after which he might be invited to undertake the Drug Treatment Programme.
As such, he remained an undue risk, Sir Ron said.
Members of the Hutchings family opposed his release and Patterson said "he could completely understand why".
He will next appear before the board in August 2022.
