(CNN) Four people were found dead Monday at a North Dakota business in what police are investigating as a multiple homicide.

The bodies of three men and one woman were found at the RJR Maintenance & Management office building in Mandan at about 7:30 a.m.

It's unclear how they died, Mandan Police Chief Jason Ziegler said at a press conference. Investigators are trying to identify the victims. There is no suspect in custody, he said.

Ziegler said that there was no evidence that the public was in danger and that so far, police believe this is an isolated incident. He didn't say what the time frame of the deaths were, citing the ongoing investigation.

RJR, which is a property maintenance and management company, posted a short statement on Facebook : "We will be closed today."

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