When Dustin La Mont stabbed two men on a suburban Auckland road, he was likely running on instincts to defend himself, a psychologist has told a court.
La Mont, 26, is accused of murdering 24-year-old Whangarei man Nathan Pukeroa outside a house in Mount Albert in the early hours of December 3 and grievously wounding Devaray Junior Cole-Kuvarji in the same knife attack.
Prosecutors say La Mont became obsessed with getting his neighbours at 21 Renton Rd evicted because of frustration with their mid-week parties and Mongrel Mob activities and went so far as to film them.
On the night of the killing, La Mont sent out a series of angry tweets about a loud party, grabbed a knife and went towards next door, the Crown says.
On Wednesday, clinical psychologist Sabine Visser told the court she believed La Mont's body had gone into "fight or flight" mode after being confronted by two large men on a dark street.
"He didn't make a rational decision in terms of deciding he was going to stand there and fight," she said.
"He didn't decide to act in an aggressive manner. He just did as part of the fight or flight reflex."
La Mont told police the men threatened him and he just defended himself - although he could not remember exactly what had happened after he pulled the knife out of his pocket.
Ms Visser said it was not unusual for him to have forgotten the confrontation, saying a stress reaction could affect memory.
She said her profile of La Mont suggested he was not aggressive and some of his behaviour - such as sneaking around his neighbours' house to video them - showed he tried to avoid confrontation.
But prosecutor Steve Hazard questioned how La Mont would have managed to open the knife in his pocket with one hand and then quickly stab both men if he was panicked.
"It might equally be the case Mr La Mont acted deliberately in the use of that knife against these two men," he put to Ms Visser, who said she could not say whether there had been "intent" on Mr La Mont's part.
The trial is in its third week.