HONOLULU -- A tour bus driver in prison for killing another driver tried on Tuesday to back out of his plea agreement.

Steve Oshiro claims he was not on drugs or alcohol and that police missed a chance to test him right after the accident.

A hearing revealed the tough bargaining that led to the plea deal.

The crash on June 12, 2006, killed soon-to-be father Corey Voss, who was driving a Toyota sport utility vehicle. Oshiro was driving the Roberts tour bus that swerved into Voss' lane and crashed head-on.

Oshiro eventually pleaded no contest to manslaughter. Facing up to 10 years in prison, he now wants out of his plea deal and to have a trial.

"Just to have 12 people come forward search for the truth and have everything come out that's really, really an important part of our Constitution," Oshiro's attorney Michael Green said.

Oshiro's prior attorney took the stand on Tuesday. He said he recommended the plea agreement after the prosecutor refused to allow pleas to lesser charges.

The prosecutor does not have a drug or alcohol test to use against Oshiro, but he does have an incriminating videotape shot not long before the accident, which showed Oshiro weaving on the road and in his seat.

If he is allowed to withdraw his plea, Oshiro is expected to say at trial that he did not want to be on the bus that day, that Roberts had overworked him and he was not impaired by drugs or alcohol, but exhaustion.

Another key piece of new evidence was that Oshiro did provide a urine sample that police did not test, which makes it hard for prosecutors to argue he hid evidence of drugs or booze.

The arguments over the deal will resume next month while Oshiro remains in prison.