WHEAT RIDGE, Colo. —The driver of a semi-truck that caused a five-vehicle crash that killed an 18-year-old driver on Interstate 70 in Wheat Ridge over the weekend was asleep behind the wheel at the time, according to a spokesperson with the city’s police department.

Those are the findings from a preliminary investigation released Tuesday by the Wheat Ridge Police Department. The crash, which occurred early Saturday on east I-70 between Ward Road and Kipling Street, shut down the highway for about 12 hours.

Denver7 News at 6 p.m.

Police said Tuesday 32-year-old Rayshawn Cox fell asleep while driving on east I-70, veering off the shoulder before flipping the vehicle. The semi then came to rest on its side, with the black undercarriage facing west.

“As traffic continued traveling east, four cars collided with the dark undercarriage,” the spokesperson said.

Inside one of those vehicles was an 18-year-old driver who was killed in the impact, police said. The identity of that driver has not been released.

Another driver was hospitalized with serious but non-life-threatening injuries, police said. The driver of the semi and their passenger were hospitalized with serious injuries and have since been treated and released.

Police said the semi was below the weight that would have required the driver to have a Commercial Driver’s License.

The police department spokesperson said they have issued the driver a summons for careless driving resulting in death, and two counts of careless driving causing serious bodily injury.

Police say this remains an active investigation and more evidence in this case may warrant additional charges.