A TV reporter and a nine-year-old girl have been fatally shot near Orlando, Florida, close to the scene of a murder that took place hours earlier.
A second reporter and the girl's mother were shot and injured by the same gunman, who is also suspected of the other homicide, police say.
The two Spectrum News 13 journalists were covering the killing of a woman in the area that morning when the teenage suspect returned, police say.
It is unclear if they were targeted.
The suspect was armed when he was arrested and was not co-operating with police, said investigators.
Spectrum News 13 identified the reporter as 24-year-old Dylan Lyons, who was killed, and photojournalist Jesse Walden who was injured.
The other two killed in Wednesday's two attacks in Pine Hills, a suburb west of Orlando, have not yet been identified.
In a news conference, Orange County Sheriff John Mina said the journalists were "in or near their vehicle", which he said did not look like a TV station's official vehicle, when they were attacked at around 16:00 local time (22:00 GMT).
He said the journalists had been reporting on a shooting that took place earlier in the day at around 11:00 local time, which saw a woman in her 20s fatally shot inside a car, when the suspect returned to the crime scene and opened fire.
After attacking the journalists, the alleged gunman - Keith Moses, 19 - went into a nearby home and shot the girl and her mother, the sheriff said.
The mother was in hospital in a critical condition, he added.