"It is very, very complicated and the serious crash unit are still some time from finishing their work with regards to the scene and measurements, calculations and speed."
Mr Allen would not say whether the driver was a relative.
"We'd like to protect his identity and that of his family as best we can."
Shane died on the narrow rural road road he had grown up on, within three kilometres of his family home.
He was one of two people on the back of the white Mitsubishi ute. The driver and another person were in the cab.
Mr Allen said it was not yet known whether the two passengers on the back of the ute were sitting or standing.
"We believe we'll be able to establish that in due course. We do know the vehicle has at some point swerved and we believe that is the reason why the deceased was thrown from the vehicle onto the road."
Police had several theories about why the vehicle swerved, but none that could be confirmed at this stage.
The ute had a standard rear tray, and the sides and tailgate were up at the time.
Crash investigators were back at the scene today taking measurements.
Late last night the vehicle was taken to a secure lock-up facility, and was being examined this morning.
Shane's parents, Jury and Amiria Hohepa, have accompanied his body to Rotorua, where a post mortem examination was to be carried out today.
A relative yesterday said Shane was due to start at Edgecumbe College after finishing at Edgecumbe Primary last year.
He was a "funny kid", who could be cheeky to fellow children, but was "just smart and cool".
He was active and liked to play touch, rugby and ride horses, she said.
A nearby resident said children often travelled on the open backs of trucks along the road, and she complained to police last year after seeing them standing in trailers being towed behind cars pretending to surf.