Mr Hepi said after about 10 minutes he heard the bike "gunning it" back to the Otiria Road property, then he heard the engine abruptly stop.
Mr Hepi and another friend ran to the crash site and found Mr Korewha, without a helmet, lying in a ditch.
He described the water his friend was lying in stained red from the blood that came from a large cut to Mr Korewha's head.
Mr Shortland said "a combination of not wearing a safety helmet, a cannabis reading of 24 micrograms per litre of blood in his system and not having a full driver's licence led to the tragedy".
He said Mr Korewha lost control of the motorcycle on a right-hand bend and the cause of death was from traumatic head injuries consistent with the motorcycle crash.
Environmental Science and Research researcher Tom Bassindale wrote a toxicology report and said the results showed Mr Korewha had smoked a cannabis cigarette 90 minutes before the crash.
"The dangers of driving after using cannabis are due to taking longer to respond to events, reduced ability to think clearly, and reduced ability to pay attention.
"The effects of cannabis may include distorted perception, difficulty in thinking and problem solving and loss of coordination."
Mr Bassindale said the level of THC, the chemical found in cannabis, in Mr Korewha's blood meant it was likely he was intoxicated at the time he died.
Mr Korewha's uncle, Daniel Korewha, told APNZ the family were devastated after the death.
He said his nephew should have known how important it was to wear a helmet when riding a motorcycle.
Daniel Korewha said the the message to wear a helmet had been drummed into the next generation "they think they're bullet proof".
"That was brought up at the tangi a lot. Helmets have saved my life a number of times."
There were lots of songs and haka about a wasted life, Mr Korewha said.
"It's just this guy knew nothing about bikes - he just jumped on in the spur of the moment and blasted off down the road.
"He thought he'd have a burn and it was his last thought. It's no good."
