Riverside firefighters .knocked down a second-alarm warehouse fire Sunday in Riverside.
The fire ignited at a warehouse at 1782 Third St. at 11 a.m., according to the department.
Witnesses told firefighters they saw a person starting the fire. Arson investigators found the person and placed him under arrest.
No injuries were reported.
Anyone with information on the fire was asked to call the fire department at 951-826-5321.