The investigation into a deadly accident near Yellowstone National Park has revealed that the pickup truck involved was responsible for the incident that resulted in seven fatalities, according to law enforcement.

Reports from Idaho State Police indicate that a Dodge Ram pickup crossed the median on Highway 20 close to Henry’s Lake State Park, colliding with a Mercedes tour van. This collision caused both vehicles to ignite. The reason for the truck veering from its path remains unknown.

“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.

Witness Roger Merrill, aged 60, was returning home when he encountered the blazing vehicles. He reported to The Associated Press that passersby were tending to the van’s survivors alongside the highway until emergency services arrived.

First responders arrive at the scene after a deadly collision between a pickup truck and tour van near Henry’s Lake State Park in eastern Idaho on May 1. (Roger Merrill via AP)

“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.

The fatal crash happened in eastern Idaho, about 16 miles west of Yellowstone National Park in Wyoming. (Getty Images)

“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.