09/02/2014 AT 06:00 PM EDT
The body of Lucius Robbi, who went missing on Aug. 19
, was found in his car on Thursday, according to authorities.
The 21-year-old University of Montana student instantly died from blunt force trauma to the head in a one-vehicle accident, Custer County Coroner Vicki Armbruster tells PEOPLE.
"The car hit a tree and went off a 60-foot embankment. This made it very hard to see from the road," Armbruster says. "A pine tree also fell on top of it, and a lot of other trees were in the area."
A helicopter spotted the kayak on top of Robbi's Subaru in thick brush and trees off Highway 21, near the turnoff for Stanley Lake, Idaho, the Custer County Sheriff's Office reports.
Recovery personnel could not see the vehicle from the roadway. It was not until the brush was removed that they got a clear view of the accident scene.
Armbruster believes the crash happened between 4:30 and 5:30 p.m. on the day Robbi went missing.
Robbi had just left his summer job guiding rafting and kayaking tours and was on his way to college when the crash occurred.
More than 3,000 people joined the Facebook group Finding Lucius
. On Friday, Tina Glaessner, Robbi's mother, posted on the page
thanking everyone for the support.
"The family of Lucius Robbi wants to thank all of the many friends who came together to search for him. You were all amazing, and the overwhelming outpouring of love and the heroic effort you made to find Lucius created a bond between you and all of us that will connect us forever," she wrote. "We are touched as well by the support of so many who did not even know our family, but showed their humanity and tremendous generosity at such a difficult time through countless acts of kindness."