Hawaii island police are investigating the death of a 5-month-old boy who sustained traumatic injuries Saturday.

Puna patrol officers and firefighters responded to a report of an unresponsive baby and met the parents on Highway 130 who were en route to the Pahoa Fire Station for medical assistance during the early morning hours Saturday, police said.

The infant was taken by ambulance to Hilo Medical Center where he was pronounced dead at 5:54 a.m. that morning.

Police said a forensic pathologist who performed an autopsy Monday indicated the baby “had evidence of life-threatening traumatic injuries.” The final determination of the cause of death is pending additional testing.

Detectives of the Hawaii Police Department’s Area I Criminal Investigation Section are investigating.

In a separate case, prosecutors charged the infant’s 21-year-old mother, Yasmine Michelle Lilia Butterfield, Wednesday after she allegedly assaulted her boyfriend Saturday night.

Butterfield of Kalapana was charged with two counts of second-degree assault, two counts of first-degree terroristic threatening, one count of abuse of a family or household member, first-degree unlawful imprisonment and interference with reporting an emergency.

Her bail is set at $43,000.

Police said Butterfield’s boyfriend, 20, reported that they were involved in an argument Saturday night regarding the death of their 5-month-old son.

During the argument, he alleged Butterfield told him that she killed their son.

When he attempted to leave their residence, Butterfield struck him several times with a wooden block and a metal broomstick, police said.

She also allegedly threatened him with a knife and refused to allow him to call for help or leave their home.

The next morning, the boyfriend reported the alleged domestic violence to police after Butterfield left the residence.

He declined medical attention.