Idaho police say truck crossed line before causing deadly tour van collision near Yellowstone National Park

The pickup truck that collided with a tour van near Yellowstone National Park last week is to blame for the crash, which left seven people dead, according to police.

Idaho State Police said a Dodge Ram pickup truck crossed the center line on Highway 20 near Henry's Lake State Park and hit the Mercedes tour van, causing both vehicles to burst into flames. It is unclear what caused the truck to leave its lane.

"Crash reconstruction is ongoing, and ISP troopers are working to determine all contributing factors," state police said on Tuesday.

The driver of the truck and six of the 14 people inside the tour van died in the crash, police said.

TOUR VAN CRASH NEAR YELLOWSTONE NATIONAL PARK LEAVES 7 DEAD, POLICE SAY

In addition to Idaho State Police, the National Transportation Safety Board is also investigating the crash since it involved a commercial vehicle. 

"NTSB personnel have visited the scene and are reviewing evidence. While information is being shared between ISP and the NTSB, each agency is conducting its own investigation," the ISP said.

Idaho state troopers responded to the tragic scene at around 7:15p.m. on Thursday, which took place approximately 16 miles west of Yellowstone National Park in Wyoming.

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Roger Merrill, a 60-year-old man who was driving home when he saw the vehicles on fire, told The Associated Press that bystanders were caring for the van survivors on the side of the highway until first responders arrived.

"It took an unnervingly long time for help to arrive just because of the location," Merrill said.

He also said he frequently sees tourist vans on Highway 20 as it leads to Yellowstone National Park.

"We extend our deepest condolences to the families and loved ones of those lost in this tragedy," ISP Sgt. Blake Higley said. "We are incredibly grateful to the passersby who stopped to help and to the first responders whose quick actions and teamwork aided those in critical need. This was a challenging and emotional scene for everyone involved."

The highway was closed for almost seven hours while first responders and the Idaho Transportation Department managed the scene and cleared the roadway.