PHOENIX -- A group of transients may have caused a fire in a vacant Scottsdale fourplex Wednesday night, said a spokeswoman for the Scottsdale Fire Department.

Fire crews quickly put the fire out, though there was extensive damage to the apartment, public information officer Tiffani Nichols said.

Nichols said crews found evidence that homeless people had used the unit as shelter and lit small fires to stay warm. The apartment was not protected by automatic sprinklers.