The Moscow-Pullman Daily News reports the fire early Sunday destroyed 88 units at the Grove complex, where many residents are Washington State University students.
The fire also destroyed three pieces of construction equipment and damaged a dozen more.
Pullman Fire Chief Mike Heston says investigators are using an arson dog. An investigator from the Bureau of Alcohol, Tobacco, Firearms and Explosives also is involved.
Pullman mayor and fire department spokesman Glenn Johnson says officials do not believe the fire is related to four unsolved arsons in the spring of last year at Washington State University.