MISSISSAUGA, Ont. -- The province's police watchdog has found there are no reasonable grounds to charge a York Region officer in relation with the motorcycle death of a 28-year-old man in June.

The Special Investigations Unit says the motorcycle driver was riding his bike around 11:15 p.m. on June 14 north of Newmarket, Ont., when a police officer in the area was investigating a report of a suspicious vehicle and travelling in the same direction.

The SIU says the motorcyclist was behind the cruiser and collided with the car as the officer was attempting a U-turn on the road.

SIU Director Tony Loparco says a forensic reconstruction of events around the collision put the motorcycle's speed at about 148 to 154 kilometres per hour just before it left a skid mark in an attempt to avoid hitting the cruiser.

He says the bike's speed at impact is thought to have been about 142 kilometres per hour.

Loparco says he suspects the bike would not have been visible to the officer if he checked the road before starting his U-turn.

"A civilian witness' evidence gives us some sense of this possibility when she recounts that the motorcycle could not be seen in her rear view mirror when she checked it 30 seconds before it passed her at high speed without any warning," he said.

"In the end, it seems that one or more of the man's speed, low lighting conditions and possible visual obstructions caused by construction work in the area, contributed to the collision that occurred."

The SIU is an arm's length agency that investigates reports involving police where there has been death, serious injury or allegations of sexual assault.