Meanwhile, family members have identified one of the victims as Dave Christianson, who was the gas station manager.
The arrested suspect was identified Thursday as Leland D. Russell, 29, whose criminal record shows previous arrests for burglary and felony harassment and a conviction for negligent driving.
King County Jail records show Russell was booked at about 12:40 a.m. Thursday and is being held for investigation of two counts of homicide. During an initial court appearance Thursday, Russell was ordered held on $2 million bail.
While police say they believe Russell was the lone shooter, a second person who was at the scene is being sought for questioning in connection with the incident, said Cmdr. Jarod Kasner of the Kent police. He said the man has been identified but Kasner declined to release his name.
The identification of the two allegedly involved in the case came from a lead developed during the police investigation, which led detectives to an address in Burien about 10 miles away from the gas station.
A SWAT team searched the home with the help of a K-9 police dog and remained there for several hours Wednesday night. By Thursday morning, the scene was clear.
Kasner says investigators aren't disclosing much other information about the case because they want to avoid false conclusions.
The apparently random double shooting unfolded at about 8:40 a.m. Wednesday at a Shell station and Wendy's restaurant in the 6400 block of 212th Street.
On Thursday morning, a candle burned near the area where two men were shot and killed. Alongside the candle are the words "My friend, you will be missed." Next to the candle are flowers.
A customer at the gas station Thursday described Christianson, the gas station store manager who was shot dead, as loving and caring. He had two grown daughters.
"I came here like every day, so it's like you know you go and see people and then the next thing you know they're gone. It's kind of weird, so it's kind of senseless, and I hope they catch the guy," said the customer, who did not want to be identified.
Witnesses at the scene, including a gas station employee and customers, told KOMO News on Wednesday that the shooter and another man had pulled into the station in a black Cadillac to fuel up, but parked in a way that blocked other customers and their vehicles from accessing the pumps.
The witnesses said the Cadillac's music was blaring loudly.
The passenger in the Cadillac got out and walked to the store, then two other men got into an argument with him outside the store about how the Cadillac was parked.
The Cadillac passenger and the two other men then got into a fistfight. When the driver of the Cadillac saw the fighting, he grabbed a gun from inside his car, ran over and shot the two men who had complained at close range, witnesses said.
The suspect and his passenger then quickly drove away from the scene, heading east on 212th Street.
Witnesses said the suspect's black Cadillac had a spare tire "donut" on the back.
The name of the second victim has not been released.