At about 3:30 a.m., the security guard saw the suspects stealing copper wire from the school at 2775 Cedro Lane. The guard chased the suspects, but stopped after one claimed to have a gun, police said.
Officers went to the school and then searched for the suspects in a nearby residential neighborhood.
About a half hour later, officers found Concord resident John Toomey, 44, who the security guard identified as one of the suspects, according to police.
Toomey was arrested on charges of grand theft, felony vandalism, possession of burglary tools and being under the influence of a controlled suspect. He was booked into Contra Costa County jail in Martinez with a bail of $25,000.
Police are still seeking the second suspect and anyone with information regarding the case is asked to call the Walnut Creek Police Department at (925) 943-5844.