King County Sheriff’s detectives said Friday that 12-year-old Jackson Roos died Wednesday as a result of being strangled by his own helmet strap while zip lining in the family’s backyard in the 8800 block of 255th Avenue Northeast near Redmond.

Detectives said a safety line attached to the cable caught on the back of his helmet, pulling it up, causing the helmet strap to tighten around his neck and cut off his air supply.

Detectives said the incident was a tragic accident that could not have been predicted. A press release issued by the King County Sheriff’s office stated, “the case is considered closed.”

People share their thoughts, memories on Facebook memorial page

Roos is described as an “amazing young man, a happy, active, loving boy.”

Those words come from the 12-year-old boy’s Facebook memorial page the day after his death.

Roos’ mother discovered him at about 2:30 p.m. on Wednesday afternoon. The Evergreen Middle School student was pronounced dead at the scene after medics attempted to resuscitate him.

The zip line was 20 feet above the ground and ran 100 feet across the yard, according to Sgt. Cindi West, King County Sheriff’s Office public information officer.

Detectives noted that the zip line appeared to be commercially made and installed; it was removed from the home for the investigation.

Kathryn Reith, Lake Washington School District director of communications, was at Evergreen Middle School on Thursday morning and noted that staff members informed students of Roos’ death when school began and counselors were on hand to speak to kids.

“It’s all about the kids. We want to make sure that they feel OK and counselors are there if they need to express what’s on their minds,” Reith said.

At lunchtime on Thursday, students wrote messages to Roos and his family.

On the Facebook page — which had 1,000-plus likes at post time — Erin Brooks Bell wrote: “Very sad day at Evergreen Middle School. Our hearts and prayers are with the Roos family.”

Jeanne Tueller Krumperman added: “I keep thinking about how a few years ago, Jackson did me a big favor and sang in the children’s Christmas choir. He was so good-natured and positive about doing it, and I am grateful I had that chance to get to know him better. Your family is in our hearts and prayers.”

Roos’ father, Bryan, owns Roos Orthodontics in Redmond; the business was closed on Thursday.