Greymouth teenager Lewis McKenzie, 18, jailed for killing of Cyrus Alupis

Cyrus Alexis Alupis, 41, died after being stabbed by Lewis McKenzie in Greymouth last July. Photo / Facebook

A grieving father says a teenage killer reminds him of his slain son and today, as the 18-year-old was jailed, urged him to turn his life around.

Scared teenage ADHD sufferer Lewis Floyd McKenzie was just 17 when he "impulsively" stabbed 41-year-old Cyrus Alexis Alupis to death in Greymouth on July 30 last year.

As McKenzie, now 18, was sentenced today at the High Court in Christchurch after admitting a charge of manslaughter, Justice Robert Osborne accepted that an aggressive Alupis had played a provocative role in the tragedy.

And Alupis' father was praised by the judge for a remarkable victim impact statement full of compassion and forgiveness for McKenzie: "that young boy".

After seeing "scary" parallels between the killer and his own son, he didn't want McKenzie to end up like his son and tied up with gangs.

"It will be a double loss if he doesn't make something of himself now," the father said.

The court heard how McKenzie and an associate had been driving around the West Coast in the early hours of July 30 last year.

They had smoked several cannabis joints before they stopped to talk to Alupis and another man just after 1am.

McKenzie and his mate agreed to give the pair a ride to Cobden where Alupis had been living.

But shortly after getting in the back seat, Alupis started to get agitated when he couldn't find a bottle of vodka.

They started driving around to look for it when Alupis accused McKenzie of having it.

Alupis threatened to give him a hiding and from the back seat, slapped him in the face and punched the driver in the head.

The driver tried to calm Alupis down but he held a cigarette lighter to McKenzie's cheek. He was frightened but not burned, the court heard.

When the teen went to take his seatbelt off, Alupis threatened to "smash him".

McKenzie grabbed a 30cm hunting knife, got out of the car, and went to the rear passenger door.

As Alupis tried to get out, McKenzie stabbed him twice - in the abdomen and chest.

He then ran off while his mate tried to drive Alupis to the hospital. The injured man kept trying to get out of the car. The driver stopped and Alupis fell onto the road. He was found soon after and rushed to hospital where he died.

At around 4.45am, McKenzie went into a supermarket and told staff he was being chased by gang members.

Noticing that he was covered in blood, the police were called. Officers found a knife in one of his socks.

Justice Osborne accepted that a "genuinely remorseful" McKenzie who suffers from ADHD had been feeling that his safety was in jeopardy when he acted quickly and impulsively.

He also highlighted McKenzie's upbringing where he was exposed to significant family violence and a childhood where he struggled with anxiety and anger.

As he was taken into custody after being sentenced to four years and two months' imprisonment, McKenzie turned to his family in the public gallery and said, "Love you whanau".