A Hamilton police officer didn't break any laws when his motorcycle collided with another one, says Ontario's Special Investigations Unit (SIU).

And the whole thing started with an unreturned nod.

Investigators say the officer didn't commit a crime when his Harley Davidson made contact with a suspect's Suzuki in 2016. The Suzuki rider suffered a fractured left arm, and was eventually found hiding under a deck.

The officer "did nothing that would justify criminal proceedings against him," the SIU said in a media release Thursday.

The incident happened around 2:25 p.m. Sept. 19.

The officer and the Suzuki rider were heading in opposite directions on the same road, the report says. The officer gave the Suzuki rider "a courtesy nod," and the man didn't nod back.

The officer turned and followed the Suzuki, the report says, and saw it go through a stop sign on Upper James Street.

The Suzuki turned onto South Bend Road with the officer following, the report says. The officer pulled up on the Suzuki's left side.

What happened next is subject to some "controversy," the report says. Either the officer's motorcycle struck the left side of the Suzuki, or the officer stopped ahead of the Suzuki and the Suzuki hit his Harley.

Either way, both motorcycles skidded to the ground, the report says, and the suspect ran away.

"He was subsequently located by police and arrested at a residence on Upper James Street hiding under a deck," the report says.

Investigators interviewed two civilian witnesses and three police officers, and took statements and notes from four others.