KAILUA — A man clubbed a woman to death with a shotgun in the middle of a residential street yesterday as horrified onlookers watched the victim crawl and scream on the roadway.

The man also struck an area resident who tried to intervene, sending him to a hospital.

Police last night arrested a suspect in Kane'ohe and opened a murder investigation. Police said the suspect, Alapeti Siuanu Tunoa Jr., 30, of Salt Lake, is the 30-year-old victim's former boyfriend and father of her child.

"He hit her two or three times like he was using an axe," said witness Ted Hardin, describing the assailant's downward, wood-chopping-type blows to the head delivered with the stock of a shotgun.

The attack took place on Maluniu Avenue near Kawainui Street, several blocks from Kailua's business district.

"Once I saw him hit her, I knew it wasn't an accident. This was domestic violence," witness Samantha Sletten said.

Hardin and Sletten said the incident began about 5:45 p.m. when they were driving south on Maluniu Avenue. A black Ford Explorer in front of them, also traveling south, was going an estimated 60 mph and ran a stop sign, they said.

The Explorer rammed the back of a white sedan, spinning it around so it faced the opposite direction.

A woman got out of the white car. The man in the Explorer ran after her and punched her, Hardin and Sletten said.

The man took the shotgun out of his vehicle and swung it at the woman. A neighbor tried to intercede but Tunoa pointed the gun at him and told the man to "step back," the witnesses said.

The assailant chased the woman around the car, caught her and hit her in the stomach with the barrel of the shotgun. The male neighbor trying to help was struck in the back of the head with the shotgun butt, the witnesses said.

"She started crawling and he went after her," Sletten said. "She was screaming." That's when the assailant hit her repeatedly in the head with the shotgun, then drove off in the Explorer.

The woman was taken in critical condition to Castle Medical Center, where she died at 6 p.m.

The male neighbor who tried to help the victim was taken to Castle in stable condition, according to Honolulu Emergency Services spokesman Bryan Cheplic.

Police arrested Tunoa at 7:05 p.m. in Kane'ohe after officers found him hiding in the yard of a home at Likeke Place. Second-degree murder charges were pending last night.

Police closed Maluniu Avenue last night and brought in portable lights to illuminate the crime scene. The white car was in the street.

Police said Tunoa, who is 6 feet 2 and 340 pounds, allegedly went to Maluniu Avenue yesterday and waited for the woman to pick up her child at a babysitter's home.

According to Hawai'i Criminal Justice Center records, Tunoa has two prior convictions: first-degree robbery in July 1996 and second-degree robbery in July 1995.

It was the second homicide this year on O'ahu, and both are believed to be domestic violence-related.

Roy William Hartsock, 40, was charged with fatally stabbing his wife, Jenny T. Hartsock, last week at their Gulick Avenue apartment building in Kalihi. Hartsock is being held in lieu of $1 million bail at O'ahu Community Correctional Center.

Reach Rod Ohira at rohira@honoluluadvertiser.com.