The Honolulu Medical Examiner’s office said today that the victim in a Big Island murder investigation died of a brain injury caused by blunt force injury to the head.

The manner of death of Joy Macres, 28, was deferred, pending further investigation, the Medical Examiner’s office said. On Sunday, Macres was transferred from the Big Island to the Queen’s Medical Center, where she died a day later.

Big Island police Lt. Gerald Wike, of the department’s Criminal Investigations Section, said detectives identified Macres’ 25-year-old boyfriend as a person of interest. He hasn’t been arrested but is cooperating with police.

Wike said police are still trying to determine the cause of the head injury and declined to say whether it was caused by an instrument or a fall.

“We’re still following up as far as reviewing the evidence that was recovered as well as statements that were made by family members and neighbors,” he said.

Police responded to a call at 4:08 p.m. Sunday from Kona Community Hospital reporting Macres had a head injury and was being flown to Queen’s.

Police wouldn’t immediately say how Macres got to Kona Hospital. 

Wike said witnesses heard an argument in Macres’ Holualoa home before she went to the hospital, but no one witnessed how she was hurt. 

Officers originally classified the case as an abuse of a family or household member. Detectives reclassified the case to second-degree murder after Macres died on Monday.