The San Mateo County Sheriff's Office said police received several calls Monday about a man in a car wearing a full gas mask with grenades hanging from his neck in downtown San Mateo, KCBS-TV, San Francisco, reported Tuesday.
The sheriff's bomb squad responded to the scene and evacuated about a half-block area around 9:30 a.m. The man was detained and the bomb squad discovered an "inert grenade" in his car.
The man, identified as Gilberto Masias, turned out to be a costume shop worker wearing an "early Halloween costume," the San Mateo Police Department said on its Twitter account.
Masias was cited for possession of an inactive grenade and released.