John Adams, 55, claimed he had been acting in self-defence when he stabbed his stepson, Joel McDonald, 38, at least 10 times to the head, chest and back on May 4 last year. One of the stab wounds had such force that it penetrated Mr McDonald’s skull.

A Supreme Court jury on Thursday found Mr Adams not guilty of murder and the lesser alternative charges of defensive homicide and manslaughter.

Mr Adams showed no emotion as Justice Terry Forrest told him he was free to leave court.

Crown prosecutor Mark Rochford, QC, had claimed Mr Adams, who helped raise Mr McDonald since he was eight years old, could have walked away from the confrontation with his drunk, angry stepson but had deliberately stabbed Mr McDonald, intending to kill him or cause him serious injury.

Mr McDonald had confronted his stepfather after his mother, Cheryl, had picked up his 11-year-old daughter to spend the day with her.

Mr McDonald had not wanted his daughter from a previous relationship to leave the house and became angry when his mother ignored him and took her.

Witnesses later saw the two men fighting in the street and at one stage Mr Adams had Mr McDonald in a headlock.

Mr Adams told a neighbour to ring triple-0, claiming Mr McDonald had attacked him with a 15 centimetre hunting knife.

Mr McDonald, who had a blood alcohol level of 0.24 and traces of cannabis in his system, died at the scene.

Defence barrister David Hallowes told the jury Mr McDonald, who was using the drug ice, could be irrational, paranoid and unpredictable.

‘‘You will remember you heard the evidence about how he would appear with the clenched jaw, the veins and those eyes like a madman, making threats to kill people,’’ Mr Hallowes said.

‘‘You heard he was someone who got into fights. And you know that he had been clearly drinking alcohol that day, clearly affected by alcohol. It made him think he was invincible, made him angry, irrational, a really angry drunk.’’

Mr Adams told police after his arrest: "I thought he was going to grab me  ... He’s a big guy and he knows how to fight. He could easily pick me up and throw me. [I] knew he wasn’t going to stop. [I thought he was] going to pick me up and dump me. [I] did not think I had any other option at the time. He was past the point."

Mr Hallowes said witnesses had given evidence that Mr Adams had loved Mr McDonald, supported him and been a good father to him, and the jury had to ask what was Mr Adams intending by his actions?

‘‘Yes, he’s striking [with the knife] but did he intend to kill or cause really serious injury?

‘‘John Adams knows that he inflicted the wounds on Joel McDonald. He knows his actions caused the death of Joel McDonald," he said.

"He will have to live with that for the rest of his life. He’s killed his stepson, killed his partner’s son. Nothing you can do will change that. That remains. What you can do is find him not guilty. What you can do is find that he wasn’t criminal in his actions that night.’’