Snohomish County sheriff's detectives have spent the past few days sorting out what happened.
Court records released Thursday detail a mess of suspects, witnesses, vehicles and weapons strewn over multiple crime scenes.
It appears the violence began earlier that day with a dispute over a marijuana purchase at the Arlington Safeway. An argument broke out among a handful of young people. The participants invited friends and family to join them for an evening fist fight at the park.
People on both sides brought handguns. The shooting was reported about 8:30 p.m. Saturday.
Emergency crews rushed Ryan Mumm, 20, to the hospital with a gunshot wound to the head. The Arlington-area man died Sunday from his injuries.
Police on Wednesday night arrested Dennis R. Watters, 41, of Tulalip. Watters reportedly told police he only fired in self-defense.
Detectives believe Watters was one of several people who exchanged gunfire. Early evidence indicates the bullet that killed Mumm came from Watters' 9mm handgun, court papers show.
Watters was being held for investigation of second-degree murder, drive-by shooting and rioting. A judge on Thursday set bail at $1 million in Everett District Court.
Several family members attended the hearing to support Watters.
Afterward, Dennis Watters Sr. said he hopes people will not pass judgment on his son until all the facts are known.
"We are grieving for two families right now," he said.
People involved in the shootout have given detectives varying accounts of what happened and who initiated separate bouts of violence. The stories, laid out in a 14-page affidavit, share some common threads.
Earlier the day of the shooting, Mumm was hanging out with a friend who drives a red BMW at the Arlington Safeway.
Mumm's friend was offered a small amount of marijuana for sale by people associated with a red Volkswagen Jetta.
Mumm's friend allegedly took the marijuana, and they drove off in the BMW without paying.
The Jetta gave chase, but the BMW got away.
About a half hour later, the two groups crossed paths along 67th Avenue NE in Arlington, according to court papers. The people in the Jetta got out and fought with Mumm and his friend.
That set in motion a volley of calls and threats between the parties. Folks on both sides called others for assistance. The groups agreed to a meetup that night at the Blue Stilly park. The dispute was supposed to be settled with fists, the affidavit said.
Meanwhile, a teenage girl who had been in the Jetta reportedly called her father and told him that the BMW driver had assaulted her, several witnesses told police.
Her father allegedly then got Watters involved.
The people associated with the Jetta met up at the Safeway parking lot. They made a plan to send other friends to the park to see if Mumm and his friends were there.
They were, and they'd also brought several friends, who were in a blue Pontiac nearby. Mumm and his friends initially grew tired of waiting, though, and were preparing to leave, police were told.
At that point, a Brown Honda showed up and reportedly rammed the BMW.
Amid the commotion, multiple people and vehicles converged on scene, including Watters, who was driving a blue Ford pickup.
People gave detectives conflicting accounts about which cars rammed which and who opened fire first. Mumm was believed to be brandishing a gun. The weapon later was reported stolen from the home where he had been staying, according to the affidavit.
Several people got out of their cars during the tussle and multiple shots were fired.
Mumm and a friend piled into the BMW and tried again to leave the park. Watters gave chase in his truck and more shots were fired, multiple witnesses told police.
The BMW's driver sped to a nearby gas station along Highway 530, where police were called and paramedics summoned. Mumm had been shot in the head.
Police have recovered multiple weapons believed to be involved in the shootout, court papers say.
Police on Wednesday surrounded Watters' home after witnesses and evidence suggested his involvement. He surrendered without incident.
He reportedly agreed to speak with detectives and that he had been reluctant to go to the fight, but his friend had "really needed him there," police wrote. He also reportedly told them that he fired into the BMW out of fear for his life and believed he'd shot Mumm in the shoulder.
His attorney, Jennifer Rancourt, argued for a low bail. She said her client has been cooperative with investigators and has roots in the community.
She questioned whether prosecutors had established probable cause to justify holding Watters for investigation of murder.
Sheriff's spokeswoman Shari Ireton on Thursday said she could not discuss specifics of the ongoing investigation.
It likely will take several weeks to collect witness statements and compare them to evidence recovered at the crime scenes, she said.
It still wasn't clear Thursday how much time elapsed between the initial argument at the grocery store and the shootout at the park. Court papers indicate at least several hours.
"There's a lot more of the investigation that needs to take place," Ireton said.
Eric Stevick contributed to this story.
Rikki King: 425-339-3449; firstname.lastname@example.org
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