Officials in Skagit County, Washington state, are working toward finding out the motive behind Friday night’s deadly shooting at Cascade Mall in Burlington, a state patrol spokesman said Sunday. The lone suspect, Arcan Cetin, is in custody and will be arraigned Monday.

Authorities searched Cetin’s apartment in Oak Harbor and recovered personal documents, electronic devices and other evidence, Sgt. Mark Francis said in a statement. No firearms were found at the residence located in a four-storied building that was marked by police tape. Investigators also interrogated the 20-year-old suspect.

Officials said that it was too early to rule out terrorism or any other motive behind the shooting.

Cetin was taken into police custody Saturday — after about a 24-hour manhunt — as he walked on a street near his house. The suspect did not attempt to run when confronted by police, Lt. Mike Hawley of the Island County Sheriff’s Office said.

“He said nothing,” Hawley said.

According to Francis, Cetin was “calm and collected last night when he was arrested.”

Officials said that Cetin, who immigrated to the U.S. from Turkey, initially entered Cascade Mall — about 65 miles north of Seattle — on Friday evening without a firearm. However, shortly after he was seen on a surveillance video with a rifle, killing four women and a man in the makeup department of the Macy’s store.

Meanwhile, authorities are working through the “scientific process” of identifying victims, Francis said. However, reports on Saturday said that 16-year-old cancer survivor Sarai Lara, Belinda Galde, 52-year-old Shayla Martin and Beatrice Dotson were among those deceased.