Deputy Prosecutor Rick Damerville said tests showed Fonseca had cocaine in his system when he was driving on a private road in the Eden Roc subdivision in Puna.

Fonseca, who leads Halau Hula 'O Kahikilaulani of Hilo, could face up to five years in prison when sentenced April 10. However, Damerville said a condition of the plea agreement in the case is that prosecutors will ask that Fonseca serve only six months in jail and a term of probation.

Damerville said Fonseca, 52, was driving left of center on the private road when his sport utility vehicle collided with a moped driven by Michael R. Spens of Mountain View at about 7:20 p.m. on Dec. 13, 2003.

An investigation showed the road was in poor condition with potholes on the right side, and that Fonseca may have been driving on the left side of the road to avoid the hazard.

Damerville said both Fonseca and Spens were traveling faster than the posted 25 mph speed limit. A police investigation showed Fonseca was driving about 40 mph. Authorities are not sure how fast Spens was traveling, he said.

Spens was riding a moped that had been illegally modified to give it more power, Damerville said. Spens had been ill, and tests showed he had also taken a medication that could have impaired his ability to drive, Damerville said.

A Big Island grand jury initially charged Fonseca with first-degree negligent homicide and driving under the influence of an intoxicant. The charge of driving under the influence was dropped under the terms of the plea agreement.

Damerville said Hawai'i law makes it difficult to prove a motorist who has been using cocaine is actually impaired. Some states have laws declaring that a motorist is automatically deemed to be impaired if that person has been using cocaine, but that is not the case in Hawai'i, he said.

Fonseca and his lawyer Andrew Wilson were unavailable for comment this afternoon.

Reach Kevin Dayton at kdayton@honoluluadvertiser.com or (808) 935-3916.