WALLA WALLA -- City police are investigating a possible arson that occurred this weekend. A resident living in an apartment in the 100 block of East Sumach Street reported waking to his smoke detector going off about 1:15 a.m. on Friday, according to a police report. The 42-year-old man found parts of his couch on fire in the living room. The man put the fire out, then found a kitchen window had been open, and a chair left outside. The man told police a pair of his shoes were also missing. Police believe someone broke into the residence through the kitchen window, and set the couch on fire before leaving.