ROCHESTER - Criminal charges were filed Tuesday against the state trooper involved in a three-vehicle crash in May that killed an 18-year-old high school student just days ahead of her graduation party.

Trooper Shane Roper was charged with second-degree manslaughter and criminal vehicular homicide related to the death of the victim, Olivia Flores of Owatonna. The Olmsted County Attorney's Office also filed charges of criminal vehicle operation against Roper related to five other people who were seriously injured in the crash.

An investigation by the Rochester Police Department revealed Roper was traveling at 83 miles per hour with his lights and siren off when he approached a busy intersection near the Apache Mall. The trooper's car slammed into the passenger side of a car occupied by Flores, who died as a result of blunt force injuries.

"Trooper Roper, violating his duty in such a gross fashion, caused the death of a young lady celebrating her impending graduation from high school," Olmsted County Attorney Mark Ostrem said in a statement announcing the charges. "Roper's conduct violated the State Patrol's Core Values. As with any other person driving recklessly and without regard to very basic rules of the road, Mr. Roper's conduct cannot be tolerated."

Ostrem said at a news conference Tuesday that Roper's job doesn't change how the county will prosecute him.

"We're going to handle it just like we handle every other case," Ostrem said.

The criminal complaint states Roper had been pursuing someone "suspected of committing a petty traffic offense" as he exited Hwy. 52 onto 12th Street SW. As he neared the intersection with Apache Mall Drive, he turned his lights off and continued to accelerate with a fully engaged throttle.

A Rochester Police Department investigation revealed Roper did not come off the throttle until the car occupied by Flores and two others started to make its turn at the intersection — just 1.4 seconds before impact.

The driver of the car suffered a liver laceration and bruised kidney, while the third occupant sustained a broken pelvis and lacerated kidney. The crash also caused both vehicles to collide with an SUV containing two occupants, both of whom suffered physical pain from the impact.

In his squad car, Roper also had a 20-year-old man who was participating in a "ride-along." He sustained bruised ribs and multiple fractures in the crash.

The investigation revealed Roper had engaged in high-speed driving without emergency lights — at one point reaching 135 mph — at least four times earlier on the day of May 18.

His disciplinary records also show he had been involved in four prior crashes involving "inattentive driving or excessive speed" while on the patrol.

"There was a consistent pattern of Roper reaching and maintaining these high speeds either without activating his emergency lights at all, or turning them off while driving at high rates of speed," the charges say.

Rochester police officials Tuesday declined to comment on the investigation, citing the open case.

Attorneys for the Flores family said they are exploring civil causes of action regarding Roper's conduct and any potential culpability on the part of the State Patrol. They are calling for an independent, third-party investigation into why the trooper was allowed to continue on the job despite his driving history and disciplinary file.

"This was an absolute time bomb — and they had knowledge of his prior driving history — and yet on the day Olivia died, he was endangering the very public that it his duty to ensure the safety of," attorney Tom Braun said in an interview Tuesday. "And the poor girl lost her life as a result of it."

Ostrem said Olmsted County attorneys plan to share information they have with the victims but won't release video to the public. He said police combed through numerous traffic and pole cameras in the area, as well as body camera footage from law enforcement who responded to the call.

Roper told investigators he was not paying attention to his speed when the fatal crash occurred, and that he believed his lights were still activated when he exited the highway.

Witnesses disputed his account, saying they did not hear or see emergency lights or sirens as the trooper reached the intersection. They described the trooper's squad car as coming in like "a rocket."

The State Patrol said Roper, who attended 13 driving training courses for a total of 107 hours over his eight-year career, remains on paid investigative leave.

"The conduct alleged in the criminal complaint is concerning and does not align with the State Patrol's core values," State Patrol Col. Christina Bogojevic said in a statement. The Department of Public Safety declined further comment.

Flores was an Owatonna High School cheerleader who was set to graduate June 7. An online fundraiser set up to support her family says, "She was fierce and she was loyal. She was beautiful down to her soul."

Star Tribune staff writer Trey Mewes contributed to this story.