Turkish-born Arcan Cetin, a legal US permanent resident, was charged with five counts of first-degree murder on Monday in a brief hearing in Skagit County District Court in Mount Vernon, Washington and ordered held on $2 million bail.
According to charging documents, while being questioned by investigators, Cetin admitted bringing a rifle into a Macy's store in Burlington on Friday evening and shooting five people.
Cetin was taken into custody without incident Saturday evening in Oak Harbor, about 30 miles (48 km) southwest of Burlington.
Cetin was described at the time of his arrest as "zombie-like" and a motive for the shooting remains unclear. The FBI previously said it had no indication the attack was a "terrorism act" but it could not rule out the possibility.
Police allege Cetin opened fire in the cosmetics section of a Macy's department store at Cascade Mall, killing four women and a man.
Surveillance video showed Cetin entering the mall without a rifle but he was later spotted on video in the store brandishing a weapon, police said. The rifle was recovered at the mall.
The attack followed a series of violent outbursts at shopping centres across the United States, including the stabbing of nine people at one in Minnesota on September 17.