No injuries were reported, but a portion of the high-end mall has been damaged.
The 240-store Westfield mall was evacuated just after 10:30 a.m. after the man, claiming to have a gun, barricaded himself inside a GameStop store and started what appeared at first to be a small fire.
"He threatened that he had a firearm, he had a backpack with him and as the employees were leaving the store they actually saw him setting a fire inside the store and then he barricaded himself in the back," said Roseville police Lt. Michael Doane.
Police and sheriff's deputies, including a county SWAT team, detained the man inside the mall. Roseville police later identified him as 23-year-old Alexander Corney Pigee. They were unable to immediately say if he had a gun.
Authorities had thought the mall's sprinkler system doused the blaze. Police later said the fire began spreading as members of the bomb squad were examining the man's backpack, forcing them to flee the building.
Even hours after the suspect's arrest, firefighters did not have a good grip on the mall fire. Crews can't fight the fire from the inside because they don't know whether the backpack the suspect left behind contains explosives as he has claimed. For now, they can only battle the blaze from the outside.
"While we want to do our job and get this fire out as quickly as we can, we also want to make sure that all of our firefighters go home tonight," said Roseville Division Fire Chief Dennis Mathiesen.
The suspect, who has been charged with arson, is believed to have acted alone. Police did not know a motive. Investigators are looking into whether two nearby fires set in the last day are also connected to Pigee.
A MySpace page by someone of the same name says he lives in Sacramento and lists his hometown as Stockton. Police said they have had contact with Pigee before, but couldn't go into specifics.
"We've had contact with him several times I suppose and the address that he's given us before has been a local transient referral type of place," said Roseville detective Jerry Wernli
One mall employee said he saw Pigee hanging around the mall earlier.
"One of our UPS drivers was the one that actually had originally seen his guy sitting on a bench while he was delivering and at that point in time realized there's something wrong with this character," said Ed Beeker, a mall employee.
The man's mother, Mary Carter, told KCRA-3 in Sacramento that her son has mental health problems and recently lost his job.
The Associated Press contributed to this report.