A total of 40 charges have been filed against a truck driver accused of causing last week's 28-car pile-up on Colorado's Interstate 70 that led to four deaths. Prosecutors allege Rogel Lazaro Aguilera-Mederos, 23, was driving a tractor-trailer when he lost control and crashed into traffic that was already backed up on I-70.

"He was operating the vehicle under circumstances where he was exhibiting extreme indifference to the value of human life," Jefferson County District Attorney Pete Weir said Friday, CBS Denver reported.

Weir said there is a "relationship" between each count that was filed and a separate individual who was was killed or seriously injured or put a serious risk of bodily injury or death. "The number of counts reflects the magnitude of the incident and the number of people that were hurt or could have been hurt by his actions," Weir said.

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The crash happened April 25 on Interstate 70 just after it descends from mountains west of Denver. The pileup involved 28 vehicles and multiple explosions. Aguilera-Mederos told investigators the brakes on his semitrailer failed.

The truck was traveling at a speed of least 85 mph in an area where commercial vehicles are limited to 45 mph, police have said.

Police also said that just before the crash the truck traveled past a ramp to the side of the highway that is designed to safely stop trucks and other vehicles that have lost their brakes.

The speeding truck had a "free and unobstructed path" to the ramp but instead swerved away from it, police have said.

The semitrailer was destroyed in the crash, making a mechanical inspection of it impossible, but investigators were trying to determine whether there might be other ways to determine if the brakes were functioning, Weir said.

Aguilera-Mederos was advised of the charges during a video court appearance Friday from the Jefferson County jail, where he remained in custody on $400,000 bond.

The charges against Aguilera-Mederos also include six counts of first-degree assault and 24 counts of attempted first-degree assault. Of the 40 charges, 36 are felonies, Weir said.