The suspect who has been arrested does have a more or less "Hispanic appearance", but is actually a Turk named Arcan Cetin:
Mall shooting suspect arrested in Oak HarborHere are the two comments
Whidbey News Times, September 24, 2016 · 7:57 PM
A suspect in the shooting Friday at the Cascade Mall in Burlington was arrested in Oak Harbor today.
The shooting in the women's Macy's store took the lives of five people and injured a woman.
KIRO reports that a deputy with the Island County Sheriff's Office noticed a man in Oak Harbor who looked like the suspect and took him into custody without incident.
Oak Harbor resident Chris Wathen said he witnessed the arrest when he was hanging out on Oak Harbor Road. He said suddenly about nine cop cars showed up near Dean's Sports Plus, officers ran out and about 30 seconds later they had the suspect in handcuffs.
Wathen said his friends recognized the man as a former Oak Harbor High School student who graduated last year.
Online records show that Cetin was arrested in July 2015 on charges of assault in the fourth degree. Initial descriptions had described Cetin as being Hispanic. According to his Facebook page, Cetin is a native of Adana in Turkey. He’s a graduate of Oak Harbor High School, class of 2015. Cetin describes his nickname as “The Turk.” As of 2014, he was in a relationship. While in high school, Cetin was in ROTC.The word "immigrant" is not used. "Native of" in stories like this is, in effect, a euphemism for immigrant.
Cetin is an active Call of Duty player.
Arcan Cetin: 5 Fast Facts You Need to Know, By Paul Farrell, September 24, 2016
He is presumably an American citizen if he was in ROTC.