The man in hospital scrubs threw the toddler like a doll from a pedestrian overpass to the freeway humming with traffic. The 2½-year-old boy fell 30 feet to the asphalt and was pronounced dead at the scene.
The horrifying incident Thursday on the highway cutting through the heart of the city shocked Honolulu residents, causing panicked parents to phone day care centers to check on their children.
Police arrested a 23-year-old man they say occasionally baby-sat the child after witnesses saw him throwing something, followed him and called authorities.
Kraig Hengst told The Honolulu Advertiser he was working in an apartment garage across the street from the overpass when he saw a man "toss the baby" at about 11:40 a.m.
"I saw the baby high in the air. I thought it was a doll at first," Hengst said. The man held the child in one arm and "tossed it into the air," he said.
One or two vehicles may have struck the boy, but it was unclear exactly what killed him, the newspaper reported.
A white sheet covered the body on the westbound lanes of the H-1 freeway, a major route through downtown that police temporarily closed. The scene was just blocks from the Capitol and the governor's mansion.
The man, who was wearing green hospital scrubs, was taken to the police station and then to a hospital, said police spokeswoman Michelle Yu. She didn't know whether he had a history of mental illness or a criminal record.
"That will be part of the investigation," Yu said.
The suspect screamed "Thank you for everything" to television crews as he was escorted to a cell block. While in a police car, he rocked back and forth in the back seat.
The Queen's Medical Center, the nearest facility with a mental health wing, declined to say whether the man was or had been a patient. But spokeswoman Rebecca Pollard said no patients were missing Thursday and none had been discharged in an unstable condition.
Johnnie Bruen told KITV that the man calmly walked away from the overpass after dropping the child. Bruen later chased the man up a hill among houses and low-rise apartment buildings near the freeway.
"He didn't say anything, he didn't scream; he looked like a normal person standing there smoking a cigarette, except that he had on a smock," Bruen said. "That's just a horrible sight that I seen down there, for any man to do that to a child."
There were no reports of a missing child, police Capt. Frank Fujii said. Officers were contacting day care centers and other area facilities to find out where the child came from.
Hedy Chun, director of a nearby preschool, Kamaaina Kids Honolulu, said 10 to 15 parents called to check on their children. All students were safe, she said, but her staff was shocked.
Gov. Linda Lingle, told of the incident shortly after it happened, called it a "real tragedy."