Washington State gun attack suspect in custody
The arrest took place in Oak Harbor, a town south-west of Burlington where the shooting happened.
Five people were killed inside Macy`s department store at Cascade Mall.
The FBI said there was no evidence that the shooting was linked to terrorism.
At a news conference, police said Arcan Cetin had been identified as a suspect after a car connected to him was seen on security camera footage at the shopping centre.
Lt Mike Hawley, of Island County Sheriff`s Department, said the car was later spotted in Oak Harbor. He said he had been on his way to the scene when he saw the suspect by the side of a road and arrested him.
Lt Hawley said the man "said nothing, he was zombie like" and was not carrying a weapon.
So far, police say they know of no motive for the shootings.
Police had launched a huge manhunt after the shootings, releasing a blurred photo of the suspect at the scene.
Three women and a girl were killed inside Macy`s while a man later died in hospital.
The Seattle Times reported that the youngest victim was 16-year-old Sarai Lara, who had survived cancer as a young child.
Her mother described her as a happy, responsible, driven student.
Police say security cameras showed the suspect entering the shopping centre without a weapon. Ten minutes later the video shows the suspect entering Macy`s with a rifle.
The gunman had fled the scene by the time police arrived.
A prayer service for the victims was held on Saturday evening at the Central United Methodist Church in Sedro-Woolley, Washington.
Five candles, one for each victim, were lit on a table in front of the church.
Burlington is about 65 miles (105km) north of Seattle.