A truck driver fell asleep at the wheel prior to a deadly crash on Saturday that left Interstate 70 closed for hours, according to Wheat Ridge police.

The crash happened at about 2:40 a.m. in the eastbound lanes of I-70 between Ward Road and Kipling Street. The driver of a large box truck, which police initially described as a semi-truck, allegedly fell asleep while driving, causing the truck to veer off the shoulder and flip over, Wheat Ridge police said in an update posted on Facebook Tuesday.

The truck came to rest on its side, with the black undercarriage of the truck facing west, toward oncoming traffic. Four cars ended up crashing into the box truck, police said, resulting in an 18-year-old man being killed. Police did not identify him.

Another driver was hospitalized with serious but non-life-threatening injuries, while the driver and passenger of the box truck were also hospitalized with serious injuries. They have since been released.

Police on Tuesday said a summons has been issued to the driver of the box truck for careless driving resulting in death as well as two counts of careless driving causing serious bodily injury. Those charges are class 1 misdemeanors. Police did not identify the driver.

The weight of the box truck was below the level that would have required the driver to have a commercial driver’s license, police said.

The investigation into the crash remains open, police said, and more charges may be filed in the future.

The crash caused heavy delays on I-70 on Saturday. The highway was closed for about 12 hours as police investigated and cleared the scene.