Firefighters responded to the fire at 17950 Hesperian Blvd. at 1:53 a.m. and found smoke coming from the roof of the 15-store strip mall, Alameda County fire spokeswoman Aisha Knowles said.
It took 40 minutes to contain the fire, which was on the roof over the Cash 4 Gold and Pretty in Pink stores.
Firefighters discovered wire-cutting tools on the roof, leading investigators to conclude that thieves were trying to remove copper wiring from the roof, causing the fire.
PG&E has shut down power to all but two stores in the strip mall, Auto Zone and Hesperian Dental, and the power will remain off until a contractor is able to inspect the wiring to determine if there is any further fire danger, Knowles said.
No injuries were reported among the 24 firefighters that responded to the call. The Alameda County Sheriff's Office is investigating the tools and evidence of theft found on the roof.
