Officials say the Roseville Galleria could be closed or limited in operations for months because of Thursday's blaze, which caused part of the roof on the building's south end to collapse.
Authorities say the 1.3 million-square-foot mall was evacuated earlier, after the man holed up in a store and started what appeared at first to be a small fire.
Police said the blaze began spreading as members of the bomb squad were examining the man's backpack, forcing them to flee the building.
Police identified the man as 23-year-old Alexander Corney Pigee.
The man's mother, Mary Carter, told KCRA-3 in Sacramento that her son has mental health problems and recently lost his job.