An unidentified attacker burst into the 103.5 FM studio as presenter Luis Manuel Medina was reading the news on air on Tuesday and shot him and station director Leonidas Martinez dead, station employees said.
Police said in a statement on Wednesday they were seeking a man named Jose Rodriguez, identified as the shooter by a witness, the station's secretary Dayanna Garcia.
Police spokesperson Nelson Rosario in a news conference urged Rodriguez "to hand himself in to be subjected to investigations, since he is the prime suspect."
Police said they were questioning dozens of other people about the attack.
In a video of the broadcast, which was streamed on Facebook, gunfire is heard as Medina reads the news and a woman's voice is heard calling "Shots, shots!"
The attacker struck at the radio station's office in San Pedro de Macoris, east of the capital Santo Domingo.
Medina was presenting the influential investigative news show "Milenio Caliente," or "Hot Millenium," on Tuesday morning.
His sister Magally Medina said he had been investigating alleged pollution of a lake by a local company.
Reporters Without Borders
Media rights groups condemned the killings.
The Caribbean nation shares the island of Hispaniola with Haiti and is a popular beach destination for foreign tourists.
Media rights watchdog Reporters Without Borders says that journalists who tackle corruption and drug trafficking in the Dominican Republic often fall victim to attacks.
"Freedom of information is also weakened by continuing impunity for crimes of violence against media personnel and the concentration of media ownership in few hands," it said in a 2015 report.
The watchdog noted that Blas Olivo, press director of the Dominican Agribusiness Association, was found murdered that year.
A television cameraman was shot dead in broad daylight in 2014 and a newspaper reporter was shot at but not hurt days before that.
Other journalists have said they were victims of hate campaigns after speaking up for the citizenship rights of Haitians born in the Dominican Republic.