LOS ANGELES — Thieves stole as much $30 million in an Easter Sunday burglary at a Los Angeles money storage facility in one of the largest cash heists in city history, police said.

Sources told our sister station KABC the theft happened at a GardaWorld facility in Sylmar.

The thieves broke into the facility undetected – without setting off alarms – by going through the roof and somehow getting into the money storage area, which may have been a vault, according to officials briefed on the investigation.

The company that owns the building did not discover the massive theft until Monday morning.

KABC’s helicopter was over the facility Wednesday and captured an apparent hole on the side of the building that was boarded up. A pile of debris was right next to it. It’s unclear if that damage is related to Sunday’s theft.

LAPD says the agency is working with the FBI on the case. It’s unclear exactly how much was stolen, but it’s believed to be one of the biggest heists in L.A. history.

The sophisticated heist leads authorities to believe that a crew of some kind is responsible for the brazen break-in. No suspect information was immediately available.

The theft comes nearly two years after as much as $100 million in jewels and other valuables were stolen from a Brink’s big rig at a Southern California truck stop. The thieves haven’t been caught.

ABC News and the Associated Press contributed to this report.