An Auckland man's relationship with an ex-business partner soured so severely that he drove to the man's home "with murder on his mind", a court has heard.
Martin Victor Lyttelton, 57, is on trial before the High Court at Auckland charged with the attempted murder of Richard Ord and causing grievous bodily harm to Mr Ord's partner, Colleen Fenton, with intent to injure her.
He has also denied a charge of aggravated burglary of the couple's North Shore house.
Crown prosecutor Scott McColgan said Lyttelton turned up at the property with a loaded .410 shotgun, spare shells and a skinning knife.
He allegedly moved through the rooms of the house, seeking Mr Ord, before he came to a locked door.
Lyttelton aimed a shot which passed through the door and struck Ms Fenton in the leg, grievously wounding her.
"Not satisfied with the havoc he had just wrought," Mr McColgan said, the defendant began reloading the firearm when Mr Ord burst through the door to confront him.
During the skirmish, the shotgun discharged into a wall and the pair allegedly struggled downstairs and into the garage.
"At some stage they reached a physical stalemate where both men were holding the gun and couldn't get an advantage," the prosecutor said.
Lyttelton then allegedly unsheathed the knife and continued the attack on Mr Ord until the police arrived.
Mr McColgan said there was a long history between the defendant and the victim.
"Their business disputes went through the courts over a period of years at great cost emotionally and financially," he said.
"Mr Lyttelton had become clinically depressed and Mr Ord became a focus for him ... he travelled to the house with murder on his mind."
But the defendant - who is representing himself - told the jury that was not his intention.
"I was labouring under a major depressive illness and intent only on suicide," Lyttelton said.
Two days before the incident he had attempted to overdose on medication and he said his judgment was "completely clouded" by his mental illness and the residual effects of the drugs on the day he travelled to Mr Ord's home.
Lyttelton said there would be little challenge to the accuracy of the Crown's version of events but stressed that he was not acting rationally.
"I apologise to [the victims] for what occurred and it's upsetting to have to bring them here for this trial," he said.
The trial before Justice Raynor Asher is scheduled to last three weeks.