Prosecutors on Friday filed 40 charges, including four counts of vehicular homicide, against a 23-year-old truck driver accused of causing a fiery pileup that killed four people on a Colorado highway last week.

Rogel Lazaro Aguilera-Mederos of Houston 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.

Defense attorney Robert Corry called the charges "excessive, duplicative and prosecutorial overkill."

The truck was going at least 85 mph (137 kph) on a part of Interstate 70 where commercial vehicles are limited to 45 mph (72 kph), police say.

Aguilera-Mederos told investigators that the brakes on his semitrailer failed. He plowed into vehicles on the crowded highway April 25 just after it descends from mountains west of Denver, setting off a 28-vehicle chain reaction of explosions from ruptured gas tanks, authorities said.

Just before the crash, police say 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 said.

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

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

The charges 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.