Someone out there knows how it happened, police believe, maybe recalls in fine detail the sights and sounds of the roadside encounter that ended Kody Williams' life.

But a year after the 19-year-old Orland man was struck on the side of the road by a hit-and-run driver, Cloverdale police are still trying to figure out who that person was.

"It's a difficult case, for sure," said police Officer Mike Campbell, who's pretty much made it his mission in life to track down the person responsible.

A $25,000 reward for information leading to an arrest and conviction in the case hasn't done the trick - yet. But Campbell seems undaunted.

"We're going to keep working it until we can't work it anymore," he said.

Williams, who'd graduated high school recently from the small community of Orland near Chico, had just arrived in Cloverdale to work with his father-in-law's construction company when he left their motel for a stroll the evening of Feb. 19, 2009.

A Sonoma County Transit bus driver found him critically injured a short time later, lying partially in the road on Citrus Fair Drive beneath the Highway 101 overpass, police said. Williams died two days later without regaining consciousness.

In the year since, Campbell said, police have not stopped working the case and continue to make progress — even if it means ruling out potential suspects.

"We've interviewed hundreds of people, and we've looked at tons of vehicles and tons of records," he said.

Campbell said he even has in mind a couple of potential suspects, but hasn't accumulated the evidence to rule them in or out.

Authorities believe Williams probably was struck at 7:47 p.m. If the car responsible was damaged, it would have been on the front, passenger side, police said.

Campbell said there are many details about the investigation that he can't disclose. But he acknowledged "a lot of highs and lows involved in a year-long investigation."

Williams' mother, Kim Sandate, said last summer that she can't understand how someone could live with the secret of causing her son's death. "I couldn't imagine waking up in the morning and carrying on with my life," She said.

Reached at the family's Orland home on the anniversary of the crash Friday, a family friend said the family was spending the weekend away, with relatives.