A Puerto Rico policeman fatally shot two high-ranking officers and a policewoman on Monday following an argument at the station where they worked, authorities said.
The unidentified suspect held a female lieutenant, a male commander and a policewoman hostage in an office before he killed them, police spokeswoman Mayra Ayala told The Associated Press.
Ayala said authorities were about to start negotiations with the suspect when the victims were killed. She said police do not yet have information on a motive.
"There are no words to describe this tragedy," Associate Superintendent Juan Rodriguez Davila told reporters.
The shooting occurred at the police headquarters in the southern coastal city of Ponce, Puerto Rico's second largest municipality. Authorities evacuated the station to investigate threats of an explosive device reported to be located in the suspect's car.
Ayala said the suspect worked in the anti-drug division and has been arrested. Officers at the scene told reporters that the victims include Lt. Luz Soto Segarra and Cmdr. Frank Roman. NBC News has not independently confirmed their identities.
Puerto Rico's police force is the second largest in a U.S. jurisdiction.