An Irwin man accused of racing another motorist in Dravosburg in September was speeding at 107 mph seconds before he crashed into a Serra Catholic school van, killing a 15-year-old student and hospitalizing four other people, authorities said Thursday.

The second driver also was speeding and fled the scene, authorities said.

“(Going) 107 miles per hour in a 40-mile-per-hour zone. At 7:25 in the morning. When kids are going to school,” Allegheny County District Attorney Stephen A. Zappala Jr. said Thursday. “Driving’s a privilege. You do stuff like this, you’re a murderer. … I think this is a murder case.”

Samantha Lee Kalkbrenner, 15, of Dravosburg was ejected from the van and died at the scene, officials said.

Allegheny County Police on Wednesday night arrested William R. Soliday, 43, and Andrew Voigt, 37, of Penn Hills in connection with what Zappala’s office plans to prosecute as a homicide.

Soliday didn’t hit the brakes on his Volkswagen Jetta until less than a second before the crash, police said. He was charged with homicide, homicide by vehicle, five counts of recklessly endangering another person, four felony counts of aggravated assault by vehicle and three driving violations, including careless driving and reckless driving, court records show.

Voigt was charged with one felony count of accidents involving death or personal injury, five counts of recklessly endangering another person and six moving violations, including careless driving, reckless driving and failure to stop and render aid, court records show.

“Any way that you look at this case, it’s a tragic set of circumstances,” said attorney Casey White, who represents Soliday. “At no point in time did Mr. Soliday act with any maliciousness. He and his family are regretful.”

State law says a person is guilty of criminal homicide “if he intentionally, knowingly, recklessly or negligently causes the death of another human being.”

Zappala joined Allegheny County Police Superintendent Chris Kearns and a cadre of police officers and investigators Thursday to explain the new charges in the Sept. 20 crash.

On Sept. 20, the two drivers were racing as they crossed the Mansfield Bridge, a half-mile span over the Monongahela River between McKeesport and Dravosburg, officials said. Soliday drove a white Volkswagen Jetta. Voigt drove a Jeep.

“They blew past me like I was standing still,” said one witness driving on the bridge at the time, according to the complaint.

The driver of the Ford school van, Richard Alan Maleski, stopped at 7:22 a.m. at a stop sign at the intersection of Third Street and Richland Avenue, according to the complaint, which cites a dashboard-mounted camera in the vehicle.

Maleski “checked traffic in both directions multiple times before traveling into the intersection,” the complaint said.

The crash occurred at 7:23 a.m. when Soliday’s Volkswagen hit the school van in the left lane of northbound travel on Richland Avenue, the complaint said.

“The impact lifts the school van into the air, spins the school van 180 degrees, and pushes the school van across each of the southbound lanes into a grass field across from Third Street,” said the complaint, citing a video from the driver of a nearby Tesla.

Soliday’s Volkswagen instantly caught on fire, Zappala said. Three students were ejected from the van, one of them landing on top of the burning hood of Soliday’s Volkswagen.

Several bystanders ran to the scene of the crash to help, Zappala said. Voigt, whose car didn’t hit the school van, did not.

“This guy just kept on going. That’s cold. That’s really cold,” Zappala said. “Good luck telling that to a jury.”

The cause of Kalkbrenner’s death was blunt-force trauma of the head, neck and trunk, according to a Sept. 20 autopsy by Dr. Todd Luckasevic. The manner of death was ruled an accident.

Maleski was taken to UPMC Mercy hospital, where he was treated for a fractured sternum, fractured ribs, neck and shoulder pain, abrasions and contusions, the complaint said.

The three juveniles, two of whom were ejected from the vehicle, were taken to UPMC Children’s Hospital of Pittsburgh, for injuries ranging from a fractured collarbone and a spinal fracture to lacerations to the face and ear, burns to the side, abrasions and contusions, the complaint said.

“Our hearts go out to all of you,” said Kearns on Thursday, addressing the families of the four juveniles. “But we are grateful for your patience as we go through this investigation. … We realize it’s taken three months, (but) we’re talking about speed, distance and time calculations.”

“Our detectives worked tirelessly to do a thorough investigation,” Allegheny County Police Lt. Venerando Costa said.

Police have not named the juvenile victims.

Authorities said they’re unsure if any or all of the four juveniles were wearing seat belts at the time of the crash. State law doesn’t require seat belts on school buses, but Serra Catholic High School would have helped to decide if they were necessary on that particular van, Zappala said.

Officials from the high school, which is in McKeesport, and the Catholic Diocese of Pittsburgh were not immediately available Thursday afternoon.

An event data recorder, similar to an airplane’s “black box,” showed that, 3.5 seconds before the collision, Soliday was driving 104 mph, the complaint said. The accelerator pedal was at 100% throttle. At 2 seconds before the collision, Soliday hit 107 mph.

Soliday applied the brakes less than a second before the crash, the complaint said.

“At the point of impact … the vehicle was going 90 mph,” Zappala said. “There are no skid marks … there are no visual barriers to explain this.”

The two drivers facing charges, who are co-workers at Bettis Laboratory in West Mifflin, were arraigned Thursday morning and taken to Allegheny County Jail, court records show. District Judge Oscar Jerome Petite Jr. denied bail for Soliday and set Voigt’s bail at $150,000, which he was unable to pay.

Soliday’s preliminary hearing is scheduled for Dec. 22, Voigt’s for Dec. 21.

Justin Vellucci is a Tribune-Review staff writer. You can contact Justin at jvellucci@triblive.com.