HONOLULU -- Former Roberts Hawaii bus driver Steve Oshiro on Tuesday pleaded no contest to manslaughter charges involved in a fatal crash in June 2006.

Oshiro was driving an empty Roberts tour bus when it crossed the center line on Kamehameha Highway in Kahaluu and collided head-on into a sport utility vehicle, killing its driver, Corey Voss.

Earlier that same day, Oshiro's tour bus got into a minor crash with a city bus. No one was injured in that crash.

In Oshiro's plea agreement, Oshiro agreed to a 20-year prison term.

"This is all the result of that man being high on crystal methamphetamine," City Prosecutor Peter Carlisle said.

Without blood tests that was hard to prove. Carlisle hired experts and interviewed witnesses who said Oshiro's twitchy behavior was consistent with methamphetamine use.

To prove manslaughter prosecutors also had to prove Oshiro knew he was dangerous before he got on the bus.

Carlisle said it is clear Oshiro knew he was impaired because he covered up an accident earlier in the morning, took a group of Kansas high school students on a terrifying ride and then told a supervisor after the fatality that if he took a drug test he wouldn't pass.

"He did not want to put the Voss family through a terrible (ordeal). This is all he can do to try and make amends, and he realizes 20 years in jail is a very long time, but there is nothing else he could do," defense attorney David Hayakawa said.

Carlisle said he will recommend Oshiro spend at least 10 years in prison before being eligible for parole.

Oshiro is facing a lawsuit from Voss' family.