Investigators are not yet releasing the name of the suspect.
Meanwhile, a Marysville neighborhood believes the search for the killer ended on their street.
The man arrested in the Conley killing was booked into the Snohomish County Jail. Investigators said he is 26-years-old, and was taken into custody at his Marysville home.
Residents of the Marysville neighborhood said that heavily-armed Snohomish County Sheriff's deputies raided the home on 58th Drive N.E. Friday to arrest a man they said has lived there for four months.
"We hear noises down at the end of the street yelling get down on the ground, get down on the ground now," Jennifer Redding said.
Witnesses told KOMO officers arrested the man after he pulled his car into the street and tried to drive off.
Marina Torres, 18, said the deputies had their guns pointed at the suspect and yelled at him to get out of the car.
Marina and her mother said an officer asked them to fill out a form relating to a homicide investigation.
The neighbors called the raid and the arrest an unnerving experience.
"If he's the person that killed this girl, I've had a killer living next to me for at least a month. It's a scary thought," Torres said.
Next door neighbors were shocked to see what was in the boxes that investigators removed from the suspect's home.
"When they opened the lids we saw what was in them and they were pretty big guns, I'm not sure what kind, but maybe rifles or shotguns," she said.
Neighbors say the man seemed quiet and waved occasionally when he was outside.
Investigators have not said whether this arrest and homicide investigation are related to the Molly Conley murder earlier this month, but Lake Stevens residents are relieved somebody's in custody.
Both Conley's father, John Conley, mother, Susan Arksey, and step-father Matthew Arksey expressed their gratitude to the detectives of the Snohomish County Sheriff's Office for their work.
Her mother and step-father also thanked those in the Lake Stevens community and the Magnolia neighborhood where they live who have supported them.