John Astor, 44, was arrested at his Walnut Creek home in the 500 block of Jones Place around 7 p.m. Thursday on charges of lewd acts with a child under 14 years old, police said.
He was booked into the Martinez Detention Facility on $1.5 million bail.
Police on Tuesday received a report of a child under 14 who was allegedly sexually assaulted in Walnut Creek recently and determined that Astor was the suspect, Sgt. Jay Hill said Friday.
Hill said the victim is not someone Astor knows through his job as a janitor at several campuses throughout the school district.
The reported sexual assault led police to investigate a past lewd act that Astor may have committed against a child, who is now an adult, the sergeant said.
Police are also looking for other potential victims "because of (Astor's) relationship with the school district ... and his contact with kids," Hill said.
Anyone who suspects their child is a victim is urged to call the Walnut Creek Police Department at (925) 943-5844.