Bond was set Saturday at $400,000 for the driver of a semi-truck that plowed into traffic on a freeway near Denver, killing four people.

Rogel Lazaro Aguilera-Mederos Lakewood Colorado PD

Rogel Lazaro Aguilera-Mederos, 23, appeared in court, where a judge set his bond at $400,000 cash or surety.

Formal charges have not yet been filed because authorities were continuing to investigate Thursday's fiery crash that also sent at least six to the hospital.

The next court hearing for Aguilera-Mederos is scheduled for May 3, when formal charges are expected to be filed, said a spokesman for the Jefferson County Sheriff’s Office.

“We believe there was some sort of malfunction, something, and there is pretty good evidence,” Aguilera-Mederos’ attorney Robert Corry told reporters after the court hearing. “This is a man who has no traffic record, no traffic offenses on his record. Not a speeding ticket, nothing like that.”

Aguilera-Mederos, who is Cuban-born and lives legally in Houston on a green card, also suffered minor injuries in the crash.

His family members told various news organizations that he had said his brakes failed.

“It cannot be overstated, the degree to which he feels sorrow for this absolutely tragic accident,” Corry said. “Everybody agrees it was an accident. Law enforcement agrees it was an accident. Everybody who has been investigating or has looked at it believes it was an accident, and it’s tragic.”

The National Transportation Safety Board was monitoring the investigation in case an opportunity to issue new traffic safety recommendations comes up.

The Federal Motor Carrier Safety Administration, which regulates and provides safety oversight for large trucks and buses, said it is also working with state and local authorities to assist in the investigation.