A Florida man has been charged with murder after police say he threw his five-year-old daughter off a bridge in St Petersburg.
A police officer saw the incident after he followed John Jonchuck Jr, 25, for speeding, Chief Anthony Holloway said.
The girl, who was dropped into 60ft (18m) of water, was found about an hour later and pronounced dead at hospital.
Police are unsure if she was dead before she landed in the water but an autopsy was under way.
Mr Jonchuck was arrested 30 minutes later after driving away. He is scheduled to make an initial court appearance on Thursday.
A report by the sheriff’s office released on Thursday revealed that Mr Jonchuck’s lawyer had met him the day before to discuss the custody of the five-year-old.
He had been acting strangely, she said, calling her God and asking her to translate a Bible in Swedish.
Twelve hours later, his daughter was dead.
Mr Holloway said an off-duty officer had been driving home when he saw a vehicle pass by him at 100mph (161km/h).
The officer, not identified, drove to catch up with the vehicle but it stopped suddenly and Mr Jonchuck got out and pulled his daughter out of the car.
Mr Holloway said the officer “thought he heard the child scream, but he wasn’t sure” as Mr Jonchuck threw her over the rail and into the strong current of Tampa Bay.
“The suspect drove off,” Mr Holloway said. “He just drove off.”
“I’ve been doing this for 29 years and I have no idea what was going on in the guy’s mind.”
The officer tried to locate the girl immediately after but could not find her. She was found 1.5 miles (2.4km) from the bridge.
Mr Jonchuck, who lives with his father, had custody of the five-year-old. He had been previously arrested, including for domestic battery in 2008 and a drink driving charge in 2013.
He had recently filed a domestic violence report against the child’s mother but it was dismissed.