Ruppert, 29, of Lake City, Fla., was last seen on Thursday skydiving in Washington, but at no time appeared to have his shoot deployed. According to a King County sheriff's sergeant, as cited by the Associated Press, if Ruppert survived the jump and was caught in a tree or lost in the forest, he probably died of hypothermia.
"We just don't think he survived at this point," Sgt. Cindi West told reporters Monday.
West went on to describe a search that covered nine square miles over four days before the ground search was suspended Sunday. "If he survived. he wasn't conscious enough to yell to us," she added.
While snow began to fall Thursday night, temperatures dipped down into the 30s and 40s around Mount Si, a steep and heavily forested 4,200-foot peak about 30 miles east of Seattle.
According to the AP, Ruppert was taking turns with two friends who were waiting at the grassy landing zone when he jumped out of a helicopter at 6,500 feet and disappeared.
Ruppert was reportedly equipped with a wing suit that allows a skydiver to glide at up to 100 miles per hour. Those capabilities make for a larger area of search ground to cover.
Ruppert had been skydiving for seven or eight years and was experienced in a wing suit, the AP reports.
The missing skydiver was last seen with a blue parachute in a black pack and wearing a tan and green wing suit, which would naturally make him hard to spot in the woods.
Friends of Ruppert's were with ground searchers over the weekend, but did not want to talk with reporters, West said.
According to the AP, which cites a friend of Ruppert’s, a memorial is taking place Monday on the mountain where he disappeared.