Authorities said Sunday what motivated the suspect to open fire at the Cascade Mall on Friday night local time remains unclear. The Federal Bureau of Investigation said it had no indication the attack was a "terrorism act," but, it could not be ruled out.

Lieutenant Chris Cammock of the Mount Vernon police department said authorities were not ready to speculate on a possible motive in the deadly mall shooting inside a Macy's department store.

"I'm not going to rule out anything at this point because we're only 24 hours [into the investigation]," he said.

Island County Sheriff's Lieutenant Mike Hawley told reporters Saturday night that he spotted 20-year-old Arcan Cetin in Oak Harbor, Washington, from a patrol car at about 6:30 p.m. Saturday (0100 UTC Sunday). He said he immediately recognized him as the suspect from earlier tips to police. Hawley said that Cetin was unarmed: "He said nothing. He was kind of zombie-like."

Few details had been released leading up to the arrest. Cetin was born in Turkey and had immigrated to the United States with his family where he is a legal permanent resident.

A man fitting Cetin's description and armed with a rifle opened fire late Friday at the Cascade Mall in the city of Burlington, about 60 miles (97 kilometers) north of Seattle. Four women and a man were killed before the gunman fled leading to a 20-hour manhunt.

"Last night we suffered an attack on our community and it really defined to me what a community is," Steve Sexton, the mayor of Burlington, told reporters, saying he was grateful to the local, state and federal authorities who had responded to the crisis. "I can't imagine what it would be like if Burlington was on its own with this. I can't imagine we'd have a suspect in custody now if we were on our own."

Washington Governor Jay Inslee, flanked by local and state law enforcement, said the entire state stood in solidarity with Burlington, a city of less than 9,000 people.

"We are united in that we know that the status quo is not good enough when it comes to violence in our communities," Inslee added.

Authorities said Cetin's family was cooperating with investigators. But since the investigation is so fresh, details about the firearm, the man's relationships and work history were not being released. He has been detained in the Skagit County Jail on a 72-hour hold and is expected to appear in court as early as Monday when he is formally charged.

A Facebook page that appeared to belong to Cetin said he was born in Adana in southern Turkey and attended Oak Harbor High School.

He posted a link to "Call of Duty," a popular first-person shooter videogame in February, in an eerie foreshadowing of real world violence.

jar/jlw (AP, AFP)