The suspects fled when officers arrived at Bellevue Memorial Park on the 1200 block of West G Street around 11:18 p.m. Sunday. They left behind the broken headstones.
Officials said three cemetery plots were damaged. Officers also found two small metal plaques that had been removed from the headstones.
Detectives said they believe the suspects were stealing the plaques so that they can sell them as scrap metal to recycling centers. The plaques would only fetch between $8.00 and $10.00, according to investigators.
The cemetery was vandalized another time in December. Thieves broke into the Bellevue Memorial Park Mausoleum and shattered the fronts of five crematory glass vaults to steal jewelry and personal belongings.
A $1,000 reward is being offered for information leading to the arrest and conviction of those responsible for the crimes.
Anyone with information was asked to contact Ontario police at (909) 395-2941.