The sheriff's department said they were working to conduct a background investigation on the Pierce County resident, whose name was not immediately released.
In a statement, his family said his "intent was not to harm anyone", referring to audio recordings of Russell talking to air traffic control during the flight.
At a news conference, officials from Alaska Airlines and Horizon Air said that they are working with authorities.
"Was doing stunts in air or lack of flying skills (that) caused crash into Island", the sheriff's office said.
Later, he said he's "got a lot of people that care about me".
He told air traffic controllers: "Those guys will rough me up if I try and land there".
The plane was a Horizon Air Q400, according to a statement from Horizon's partner airline Alaska Airlines.
Officials said he was a 3.5-year Horizon employee and had clearance to be among aircraft, but that to their knowledge, he wasn't a licensed pilot. At that speed, the F-15s could have reached the Q400 in less than five minutes after take off from Portland.
Rate the players (v Derby Country)
And while Leeds 'keeper Bailey Peacock-Farrell definitely could have done better, there's no denying the quality of the hit. The 25-year-old striker still had a lot of work to do when he received the ball from Klich in a crowded penalty box.
Normal operations at the airport were interrupted for a time by the unauthorized takeoff but have resumed, the airport said in its tweet. As often happens in situations like these, some information reported early may turn out to be inaccurate. Preliminary info is that a mechanic from unknown airlines stole plane.
He crashed the plane in a wooded area of Ketron Island, 25 miles south of Seattle-Tacoma International Airport.
Mr Russell, a ground service employee with Horizon Air, has not been officially named by authorities but his family have revealed his identity.
He had no objective to be at that plane Friday evening "other than. what he did do", Tilden said.
In one, the controller can be heard telling the pilot: "What we don't want to see is you get hurt or anyone else get hurt, so like I said, if you want to land, that's probably the best way to go". "It's going to disappoint them to hear that I did this", Russell said at one point.
Moments later Russell crashed the plane onto the sparsely-populated Ketron Island.
Law enforcement officials stand at a staging area, Friday, Aug. 10, 2018, at the ferry terminal in Steilacoom, Wash., near where a Coast Guard spokeswoman said the agency was responding to a report of a smoke plume and possible plane crash. On Friday around 7:32 p.m., he got in the cockpit of an empty 76-seat Horizon Air turboprop plane and took off without authorization.
Jeremy Kaelin said he worked with Russell, a ground service agent at Horizon Air, in 2016.
Experts say the crash exposed alarming gaps in airport security, and is likely to prompt a major review industry security measures.