GRANITE FALLS—On July 11, 2006, Mary Cooper, 56, and her daughter Susanna Stodden, 27, went hiking on the Pinnacle Lake Trail near Granite Falls. Later that day, mere hours after they had left their home early that morning, they were both found shot dead in the head on the trail.

Both of the women’s clothing had been partially removed. Mary’s husband David suspected it was an attempted sexual assault that had gone wrong telling reporters working for King 5 back in January that they were both “pretty strong people.”

David was a suspect for a long time and was even given a polygraph test, which he passed. Infuriated by the Snohomish County Sheriff’s Office, whose investigation he called a “failure” in an Everett Herald advert, he decided to take measures into his own hands.

David Stodden worked on a documentary film about the murders, teaming up with Seattle-based Investigative Films and is now offering a $1,000 reward for anyone who can forward with information that will solve his wife and daughter’s murder.

Detectives working for the Snohomish County Sheriff’s Office 18 years later, are still seeking tips that could lead to solving the cold case.

The Pinnacle Lake Trail is in the Snoqualmie-Mt Baker National Forest off the Mountain Loop Highway, east of Granite Falls and Verlot.

Mary Cooper and her daughter Susanna’s ashes were sprinkled on Mount Kilimanjaro in Africa, the Grand Canyon, the Colorado River, and at the home garden in the Seattle neighborhood of Green Lake. There was an estimated 1,500 people at their memorial service.

Mary was a school librarian and was described by family as being a “voracious reader.” When she was growing up her father took her on plenty of hikes and she decided to raise her children the same. Susanna, her daughter, quickly followed suit and formed an avid bond with the great outdoors.

Susanna had just turned 27 a week before she was killed. She graduated from Western Washington University with a degree an Environmental Studies in 2011 and spent a semester teaching in Nepal before returning to Seattle to work in a non-profit that teaches children about nature.

The mother and daughter had spoken about their plans of hiking Mount Pilchuck leading up to that fateful day with Mary’s women’s group. During that group, Mary had mentioned how excited she was to spend a day hiking with her first-born daughter.

It was reported that the mother and daughter changed their itinerary that morning, deciding to hike Pinnacle Lake instead out of fear there would still be snow on Mount Pilchuck.

It was an early morning and there were very few cars in the parking lot that day. Before embarking up the trailhead, Susanna and Mary spoke to a couple right outside the parking lot, who told officers they remember hearing what sounded like “thunder” up the mountains, wondering if what they heard were gunshots.

Mary and Susanna’s bodies were found by a hiker around 2:30 p.m. that day. He hurried back to a nearby campsite to call for help.

Back in Seattle, David Stodden began to grow worried the later the day grew. He called the Washington State Patrol and the Snohomish County Sheriff’s Office. He recalls Officers showing up and being questioned, his car’s odometer read, before they broke the news.

David cooperated with the police, turning over computers, checkbooks, and life insurance policies. He has not stopped seeking to solve the murder of his wife and daughter.

David and Mary met each other while studying at the University of Washington. They had been married for 30 years.

Anyone with information or tips related to this investigation is asked to call the Sheriff’s Office tipline at 425-388-3845.