Detectives are investigating a tip that the suspect in a deadly mall shooting north of Seattle may have tried unsuccessfully to purchase a handgun just hours before the slayings occurred.

Authorities say Arcan Cetin used a .22-caliber Ruger rifle when he opened fire Friday at the Cascade Mall in Burlington, Washington, killing five. Cetin's stepfather told detectives after the shootings that his Ruger rifle and .22-caliber ammunition were missing.

Skagit Multi-Agency Response Team spokesman Sgt. Mark Francis said Thursday that authorities are investigating whether the 20-year-old tried to buy a weapon from a gun store and are reviewing store video.

Cetin, who has a criminal record dating back at least two years and was charged last year with assaulting his stepfather, was under a court order not to possess firearms.