The driver whose car plunged off a cliff near Wairoa last November, killing himself and two passengers, was trying to block another car from overtaking and had meth in his blood, a coroner has found.
Driver Ronald Rigby, 53, was killed in the crash, along with Terry Stone, 31, and Nathan Isaac, 29.
The men were on their way to the Mongrel Mob gang's 50th anniversary celebrations in Hastings
After the crash, police said they were investigating if the car had been run off the road.
A spokesperson for the Mongrel Mob said there were subsequent clashes with Black Power members.
"The tension in Wairoa is okay, but there are factions around the country and the news has come back to us that little incidents have started to happen, just little clashes between the two groups," said Rex Timu.
A coroner has now found Mr Rigby had methamphetamine in his blood at the time.
Chris Devonport found the driver crossed the centre line to stop a car overtaking him, the two vehicles made contact, and his car crashed over a barrier and down a 125 metre bank.
"[Rigby's car] mounted the barrier at the side of the northbound lane at an angle of approximately 20 degrees, mounted the barrier and made contact with the ground a short distance from the edge before tumbling down a near vertical bank about 125 metres into the Mohaka River," Mr Devonport found.
The other car was found days later by police but the identity of the driver was never discovered.
A fourth man in Mr Rigby's car survived.