A speeding semitrailer whose driver was described by one witness as "wide-eyed" and "terrified" passed a truck ramp before plowing into other vehicles on a crowded highway near Denver, killing four people and injuring at least six others, according to court documents released on Saturday.

The truck driver, 23-year-old Rogel Lazaro Aguilera-Mederos, of Houston, made his first court appearance Saturday after being arrested on suspicion of vehicular homicide.

State District Judge Chris Zenisek set the driver's bond at $400,000. Aguilera-Mederos, who suffered minor injuries in the crash, didn't speak during the hearing. He was represented by Denver attorney Robert Corry, who couldn't be reached for comment afterward.

Deputy District Attorney Kate Knowles had recommended a $500,000 bond, citing Aguilera-Mederos' status as a green card holder from Cuba with no ties to Colorado and the seriousness of the wreck.

His next court hearing is set for May 3, when prosecutors are expected to file charges against Aguilera-Mederos, who remains in the Jefferson County jail.

The fiery crash happened Thursday on Interstate 70, where the highway descends from the Rocky Mountains, and involved 28 vehicles.

According to the arrest affidavit in the case, Aguilera-Mederos told investigators that his brakes had failed on his truck that was hauling lumber and he noticed his truck was traveling 85 mph before the crash.

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However, other motorists told police that the truck seemed to be traveling faster, with one witness estimating as much as 100 mph (160.9 kph).

In addition, two witnesses in another truck said they saw fluid coming from the rear of the trailer on the truck driven by Aguilera-Mederos.

According to the affidavit, Aguilera-Mederos' truck passed a sign advising drivers of a runaway ramp, which enables vehicles that are having braking problems to safely stop, 2,000 feet (609.6 meters) ahead and had a "free and unobstructed path" onto the ramp but instead swerved away from the ramp, which is located off the side of the highway.

A speed limit sign on that stretch of road limited commercial vehicles to 45 mph.

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Aguilera-Mederos told police that he tried to activate emergency brakes without success and that just before his truck hit other stopped vehicles he thought he was going to die so he "closed his eyes," the affidavit says.

One driver whose vehicle was passed by the speeding truck said he saw that "the driver of the semi was 'wide-eyed' with a terrified look on his face."

After the collision, he crawled from the truck as fire began to engulf the crash scene, triggering explosions and a blaze so intense that it melted the roadway and metal off cars.

The interstate was closed for nearly 24 hours before completely reopening Friday night.