(CNN) Four firefighters were injured and a body was discovered in a Califorina fire that police believe was intentionally set.

Firefighters were called Sunday to a commercial building in downtown San Jose to respond to a report that a disgruntled former employee or former tenant was threatening to start a fire in the structure, San Jose Fire Captain Mitch Matlow said.

When firefighters arrived, smoke was already billowing out of the building, which had retail space on the ground floor and residential space on the upper floors, Matlow said.

Four firefighters were transported to a local hospital in unknown condition after suffering injuries.

Responders also found a body in the fire that they believe is the man who threatened to start the blaze.

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