SKOWHEGAN – A mentally ill Portland man who is accused of killing a cabdriver in Pittsfield in February might never be tried for the murder as his level of competency continues to be evaluated.

The man already has been diagnosed with schizophrenia, and his condition was exacerbated earlier this year when he suffered a serious head injury while a patient at Augusta Mental Health Institute.

Derek-Finn Wilhelmsen, 21, twice has been found incompetent to stand trial, according to his Waterville attorney, M. Michaela Murphy. This status was determined after evaluations by a forensic psychologist hired by Murphy and a state examiner. Both experts agreed the man was incompetent.

Murphy said Wilhelmsen had a new neurological examination June 25 and was found competent to be arraigned. That action, however, was postponed for several months as Wilhelmsen recovered from a head injury he suffered in May at AMHI.

On Wednesday, eight months after Wilhelmsen was arrested, he continued to be evaluated. “We are waiting for the last part of the state’s evaluation,” said Murphy. “We have received the psychiatric results and are waiting for the psychological results.” Murphy said the doctor responsible for that examination was seriously ill and the task had to be delegated to another doctor.

Murphy said that once all the testing has been completed, the state prosecutors would decide whether to proceed with a murder trial or settle the case “by agreement.”

In May, Murphy said, she went to AMHI, where Wilhelmsen has been held since February, to interview him before his scheduled arraignment. She found him lethargic and injured. Murphy said AMHI officials had not told her that her client was injured.

She categorized her client’s head injury as “partially self-inflicted.” She would not elaborate on the situation but said he had a concussion, among other things, and “some real brain injury.”

Wilhelmsen is accused of shooting Portland cabdriver Nunzi Mancini, 38, several times in the head and shoulders as Mancini sat behind the wheel of his taxicab the night of Monday, Feb. 11.

According to court documents, Mancini had given Wilhelmsen a ride to Pittsfield, arriving at Route 100 about 8:30 p.m. 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 murder. 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.