Police released an image of the man who is believed to be the suspected gunman:

Here is the shooter. We believe just one shooter. Notify authorities if you see him. Armed with rifle.
We're actively searching for suspect, tracking leads, etc
EMS starting to enter to attend to injured inside Mall w/ police escort and after initial clearance.

Here's a map view of Cascade Mall:

cascade mallA map view of Cascade Mall in Burlington, WA. Google Maps

And here's some video from outside the mall:

The Cascade Mall is an enclosed shopping center that opened in 1990, according to the mall's website. It features JC Penney, TJ Maxx, and Macy's stores, among others — including some restaurants and a movie theater.
Washington Gov. Jay Inslee released a statement on the shooting late Friday, saying, "Tragedy has struck in Washington tonight. Our hearts are in Burlington."
The shooting follows an incident at a mall in St. Cloud, Minnesota, in which eight people were injured in a mass stabbing on Saturday. A suspect with a knife who was dressed in a private security uniform made references to Allah while attacking at least eight people there. The suspect was shot dead by an off-duty police officer, authorities said.
ISIS claimed responsibility for that attack.