A third suspect has been arrested in connection with the fatal shooting of an off-duty Monterey Park police officer during a botched robbery attempt in Downey, police announced Friday.

Gerardo Magallanes, 18, of San Pedro was arrested Thursday and booked on suspicion of murder in connection with the fatal shooting of Officer Gardiel Solorio, 26.

Magallanes’ alleged role in the shooting was not specified.

Solorio was in his vehicle in the parking lot of an LA Fitness gym in the 12700 block of Lakewood Boulevard, near the Glenn Anderson (105) Freeway, around 3:30 p.m. Monday when a suspect — later identified as 20-year-old Carlos Delcid — allegedly got out of a car nearby and approached Solorio with a gun drawn in what appeared to be an attempted robbery, prosecutors said.

Solorio attempted to flee by backing up his vehicle when the suspect fired multiple times, officials said.

Delcid was arrested on charges of murder, attempted robbery and being a felon in possession of a firearm. A 17-year-old suspect who was allegedly driving the getaway car was also arrested and charged with a single count of murder in Compton Juvenile Court.

Funeral arrangements were still pending for Solorio, a rookie officer just weeks out of the academy. Monterey Park Police Department Chief Kelly Gordon called his killing “a senseless act of violence.”