Snohomish County investigators explained Monday what led them to arrest a Marysville man in the shooting death of a 15-year-old Seattle girl last month.

Molly Conley was visiting friends in Lake Stevens and celebrating her birthday June 1 when she was struck in the neck by a bullet. Several of her classmates were with her at the time.

Erick N. Walker, 26, was arrested at his Marysville home Friday. He was booked for investigation of first-degree murder, drive-by shooting and assault with a weapon.

According to probable cause documents, there were other reports of shots fired at homes in the same general area as the Conley shooting. At one of those scenes, a vehicle was allegedly hit by the suspect vehicle.

Paint chips from the damaged victim vehicle were sent to the Washington State Patrol crime lab to determine what kind of vehicle had hit it.

Investigators cross-referenced that with purchase records from the Tulalip Cabela's, looking for the type of weapon they believed was used in the shootings -- a 30 carbine caliber. That ultimately led them to Walker.

Arnie Faulkner nearly came face to face with Walker. Faulkner had heard gunshots around his home and came out to investigate. He couldn't believe what he saw.

He ran by me headed south holding rifle in his hand. There was no mistaking it was a rifle, said Faulkner.

The probable cause documents show investigators learned from Walker s Facebook page that he worked at Boeing in Everett. After contacting the company to confirm Walker worked there, detectives found a 2006 Pontiac G6 coupe in a Boeing parking lot that was registered to Walker. The vehicle allegedly showed signs of damage consistent with what happened on June 1.

The Snohomish CountySheriff's Office has not yet revealed a motive for the shootings.

Investigators say four police agencies were involved in the case. A dozen witnesses provided information, but police said no single tip led the arrest.

Molly's family released this statement Monday:

Our Daughter and Sister Molly Conley was shot and killed June 1st in Lakes Stevens while celebrating her 15th Birthday with friends. As this tragedy unfolds we ask the media and public to recall the beauty, grace and love that is Molly. She inspired classmates, inspired teammates and opponents, and inspired her family to live better lives, to find hope in the midst of hardship, and to play the game--whether soccer, lacrosse, or life--with enthusiasm, determination, and joy. She is the reason we are here today, and it is her life, more than her death, that we hope people will remember; since it is her life that was so amazing.

The violence that took her life and the circumstances that caused another human being to commit such an act are compelling and all want to understand it. As this aspect of Molly s story is examined do not lose sight of our daughter and sister; continue to honor her and present her shining example.

We thank the media for respecting our privacy and grieving. We are grateful to the Snohomish County Sheriff s Department, especially Detective Brad Pince and Under Sheriff Tom Davis, for their ongoing dedication and kindness to us during this horrific time. Their efforts bring great relief to our family and the Lake Steven s community. We are grateful for the outpouring of support from Lake Stevens and surrounding communities who s contributions toward Molly have been so helpful.

We continue to appreciate the generosity and love shown to us by our friends and relatives, our Magnolia and Kenmore communities, and all those that loved Molly and have been inspired by her beautiful life.

Susan Arksey, John, Tara, Johnny Conley, Mathew Arksey

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