SKOWHEGAN – The man accused of killing a taxi driver in Pittsfield in February 2002 waived his right to a jury trial Wednesday at Somerset County Superior Court, setting the stage for a trial in front of Justice Nancy Mills beginning May 12.

Derek-Finn Wilhelmsen, 21, is accused of shooting Portland cabdriver Nunzi Mancini, 38, several times in the head and shoulders as Mancini sat behind the wheel of his cab in a driveway on Route 100 in Pittsfield.

M. Michaela Murphy, Wilhelmsen’s attorney, said that psychological and psychiatric testing done by the state since her client’s arrest will show that he was unable to control his behavior. Wilhelmsen’s tests show “there are issues of criminal responsibility,” Murphy said.

In the years before his arrest, Wilhelmsen had been diagnosed with schizophrenia, and his condition was exacerbated last summer when he suffered a serious head injury while a patient at Augusta Mental Health Institute, according to Murphy. The Portland man twice has been found incompetent to stand trial, determined after evaluations by a forensic psychologist hired by Murphy and a state examiner. Both experts agreed at the time the man was incompetent.

Despite continuing issues about Wilhelmsen’s mental status, the trial will proceed as scheduled.

According to court documents, Mancini had given Wilhelmsen a ride to Pittsfield, arriving about 8:30 p.m. Feb. 11. Wilhelmsen told detectives he had gone to Pittsfield to kill his former girlfriend, Amy Towle, and her baby. Distraught over his recent breakup with Towle, Wilhelmsen apparently turned on Mancini after the cabdriver called Towle a vulgar name. Mancini’s body was found by a Pittsfield police officer early the next morning.

After allegedly killing Mancini, Wilhelmsen got a ride to the Concord Trailways bus station in Bangor from Towle, who was staying at a home nearby and was unaware of the slaying. He was arrested later the next day after he returned to Portland and sought mental health services.

Wilhelmsen told police he planned to kill himself with the gun he used in the slaying of Mancini, a .22-caliber handgun he had hidden in a backpack at his Portland apartment building. Police recovered the gun.