A truck driver who crashed into stopped traffic on a Colorado interstate last week, setting off a wreck that killed four people and seriously injured two others, was formally charged Friday with three dozen felony counts. He potentially faces decades in prison, a prosecutor said.

Rogel Lazaro Aguilera-Mederos, 23, is charged with 40 counts, including six counts of assault in the first degree and four counts of vehicular homicide, in the fiery April 25 crash on I-70 eastbound near Denver.

District Attorney Pete Weir said Aguilera was "driving extremely fast and in a reckless manner" in an area where the speed limit for commercial vehicles is 45 mph. The semi Aguilera was driving was estimated to have been going "in excess of 85 miles an hour," the DA said.

"Mr. Aguilera was observed by a number of citizens driving recklessly, swerving through various lanes of the road,” Weir, the district attorney for Jefferson and Gilpin counties, said at a news conference Friday.

The truck with a trailer crashed into eastbound traffic that was stopped because of an accident ahead, and the crash caused a fire that engulfed vehicles. The crash, which occurred in the city of Lakewood west of Denver just before 5 p.m., involved 28 vehicles.

Aguilera, who suffered minor injuries, told police that he was going 45 mph, his brakes failed and the downhill grade caused the big rig to accelerate, and that he tried the emergency brakes, according to an arrest warrant affidavit.

He said he attempted to maneuver to the right shoulder to avoid stopped traffic, and when he saw that shoulder was blocked by another stopped semi-truck he swerved back into lanes of stopped traffic, according to an the affidavit.

Aguilera allegedly said that he thought he was going to die and closed his eyes before hitting stopped traffic, according to the affidavit. Another driver on I-70 who saw the semi speed past told police that the driver was "wide eyed" with a terrified look on his face, according to the document.

Rogel Lazaro Aguilera-Mederos Lakewood Colorado PD

Aguilera, who is Cuban-born and lives legally in Houston on a green card, has a valid commercial driver's license out of Texas, officials said.

His attorney, Robert Corry, did not immediately return a message seeking comment late Friday afternoon. Corry told reporters last week that it was a tragic accident.

"Everybody agrees it was an accident,” Corry has said. “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."

"We believe there was some sort of malfunction, something, and there is pretty good evidence," Corry said, adding that Aguilera has no traffic offenses on his record, not even a speeding ticket.

The DA said Friday that the semi-truck was completely destroyed, making a mechanical inspection impossible. "There will be other means by which hopefully we can determine whether or not brakes were a cause of the accident, or some other cause," he said.

Killed in the crash were Doyle Harrison, 61, of Hudson; William Bailey, 67, of Arvada; Stanley Politano, 69, also of Arvada; and Miguel Lamas Arrellano, 24, of Denver, Weir’s office said in a statement. Four others were injured, including two who suffered serious injuries, the prosecutor said.

Aguilera is charged with six counts of first-degree assault; 24 counts of attempted first-degree assault; two counts of vehicular assault and and four counts of vehicular homicide, Weir said.

Aguilera is also charged with one count of reckless driving and three counts of crime of violence. He is being held in lieu of $400,000 bail.

"Potentially Mr. Aguilera could be looking at decades in the Department of Corrections," the prosecutor said.

Lakewood Police Chief Daniel McCasky on Friday called the wreck the most serious he’s seen in over three decades in law enforcement.

"I have never seen anything like this, and I think probably talking to our investigators most would agree — we have not ever had an accident of this magnitude, or a crash of this magnitude,” McCasky said.