MILILANI — It's a moment that he can't forget, the moment his teenage buddy — Robert J. Hartsock — slipped off the edge of a cliff and fell to his death.

Noel Bueno, a 9-year-old boy going on something much older today, was only a few feet away from Hartsock, close enough to see him clawing at the ground for balance Thursday afternoon.

The next moment his friend was gone.

Hartsock, a 15-year-old Mililani boy, died when he fell off a cliff at Waikakalaua Ditch. The ditch, with its shallow streambed below, runs along the American Classics subdivision in Mililani Mauka.

"You could hear branches break, you could hear a splash at the bottom," Bueno said yesterday in the living room of his Mililani home.

An autopsy yesterday by the Honolulu medical examiner determined the cause of death was multiple internal injuries due to a fall, and was ruled an accident.

Hartsock and five other boys, all good friends, had gone to play on the slope behind the new homes near Ho'olu and Kelakela streets.

Hartsock, who would have been a sophomore at Mililani High School this fall, was a leader among his peers and his fun-loving attitude always relaxed everyone, his friends said. His passion was skateboarding but the athletic teen also loved to box and play basketball and football.

"He always used to play with us and watch over us, like tell us not to do any dumb things," Bueno said.

Bueno's mother, Mona Shen-Bueno, said Hartsock was "very protective and would watch out for you."

"He was like part of the family," Shen-Bueno said.

Hartsock was Bueno's neighbor in the Havens of I'i Vistas, which is less than a mile from the ditch. He was a popular youth in the complex, well liked by just about everyone.

"He was very gentle, real soft-spoken, a good role model," said his neighbor, Hugh Dusza, a pastor at Mana'o'i'o "Faith" Baptist Church, where Hartsock often attended.

Another neighbor, Alvin Paguio, hired Hartsock about a year ago to deliver The Advertiser. The teen would work on vacations and Sundays, Paguio said.

"On Sundays he was like a little assistant manager," Paguio said. "He went out and serviced missed deliveries. He would ride his bike all over Mililani Mauka to get them their papers."

Hartsock and his friends never thought the ditch was dangerous.

But Launani Valley resident Lydia Snook said yesterday that she had warned the boys three times since mid-May that the area was dangerous. Each time the boys were respectful, but they ignored her, she said.

Snook was concerned about a small cliff that the boys would often sit on, she said.

"I would say, 'Get back off it, it is dangerous. You could fall and hurt yourself,' " Snook said.

Snook had felt so strongly about it that she shared her concerns Wednesday evening at a meeting of the Launani Valley Community Association, which is the master association of seven homeowner associations in the valley.

When Snook saw the boys about 1:30 p.m. Thursday, she was going to call police, but changed her mind after they turned around. Then the boys began to argue and the oldest among them — Hartsock — headed toward the cliff, Snook said.

Foliage in the area blocks Snook's view of the cliff from her home, and when Hartsock disappeared behind it, she felt something was wrong. After a few minutes she called police. She was told someone had already reported that Hartsock had fallen.

Snook ran out behind her backyard and could see Hartsock in the streambed.

"It is tragic," she said. "Perhaps it could have been avoided. I took action. I just had that feeling. I wanted to have the police yell at them. I wanted to have the police talk to them so that it could have been prevented."

Charlie Remington, association manager for the Launani Valley Community Association, had listened to Snook's concerns Wed-nesday night and yesterday said he had planned to contact Castle & Cooke, the landowner building homes in the area.

"It is unfortunate circumstances," Remington said. "Boys will be boys. I remember my days when I used to experiment and go hiking around. That's what these kids were doing."

In a statement released yesterday, Castle & Cooke said: "We are deeply saddened by this tragedy and extend our deepest sympathies and condolences to the young man's family and friends.

"We will assist authorities in any way possible with their investigation into the circumstances involving this accident. At this time, we do not know all the facts leading up to this accident. However, as a precautionary measure, we are installing additional warning signs and construction fencing."

Remington said the cliff height is not 90 to 100 feet as reported by police, but rather 35 to 45 feet above the streambed. He said most of the ditch slopes down at a 45-degree angle.

"But where they were just happened to be hard-packed clay and it is slippery," he said.

Castle & Cooke had not determined yesterday if Hartsock fell from its land, said company spokesman Carlton Ching.

Area residents have reported that Hartsock and the boys he was with had gotten onto the slope above the streambed by walking behind a new but unoccupied home near Kelakela and Ho'olu streets.

"We understand the children found a plateau down the slope, and they got there and were congregating there," Ching said. "We understand there are hiking trails back there. We are still not sure how the children got behind there."

Ching said the streets nearby are a mix of occupied and unoccupied new homes, and the entire area is considered a Castle & Cooke construction site until it is completed.

Workers said that they often see new home owners and children in the area and wouldn't necessarily chase any of them away, Ching said.

"Unless they are getting close to any construction or any heavy equipment or are in danger, nobody from a construction crew will say please leave the premises," Ching said.

Reach Mike Gordon at mgordon@honoluluadvertiser.com and Robert Shikina at rshikina@honoluluadvertiser.com.