It is not clear why Trevor Heitmann roared down a San Diego highway in the wrong direction as his speedometer approached what was likely triple digits.

What is known is this: Heitmann smashed his McLaren sports car into another vehicle Thursday afternoon, killing a woman and her 12-year-old daughter. The girl’s brother described her as a bright girl who was to start seventh grade within days.

Heitmann, 18, also died in the crash, which erupted into a fireball as other drivers smashed into flaming wreckage strewn across the highway lanes. The San Diego Union-Tribune reported that Heitmann drove a 2015 McLaren 650S.

His vehicle “disintegrated,” California Highway Patrol officer Jake Sanchez told the paper, calling the McLaren line of exotic sports cars among the fastest on earth. Heitmann could have exceeded 100 miles an hour before the collision, Sanchez said.

Heitmann, a YouTube star known online as “McSkillet,” bought the car with money he made from monetizing videos and popular online-game-model trading. Similar models can surpass 200 mph, the company says.

Local news footage captured the burned-out frame of the Hyundai SUV driven by the woman. Another person was seriously injured when they were struck by debris, authorities said.

The San Diego County Medical Examiner’s Office confirmed Heitmann’s death but did not confirm the names of the mother or child who were killed.

Dominic Pizarro, 22, the woman’s son, identified her as Aileen Pizarro, 43, and his sister as Aryana, the newspaper said.

“She was a girly-girl, but she was also tough,” he said of his sister. “She was alive with energy.” In their last video chat, his sister showed Pizarro her new school supplies.

His mother was a counselor who helped children cope with abusive homes, he said.

“She loved to work with them and tell them they were worth something,” Pizarro said. “She went out of her way to bring light to them in hopeless situations.”

He started a GoFundMe to aid in funeral costs.

Heitmann bought the sports car with the profits from trading custom models of items, called skins, for the computer game “Counter Strike: Global Offensive.” In December, he posted a video of the McLaren he bought, explaining that he used funds from skin trading and monetizing YouTube videos.

Friends speculated on social media that Heitmann had struggled with mental-health issues before the incident. One person who identified himself as a friend said Heitmann had been grieving, according to the gaming website Polygon.

“Everyone please spread love and support, he was battling an incredible rough time and we need to show support,” the friend said.

The thread became a debate over what kind of condolences should be shared.

“If the news is accurate right now he killed two people in the process of killing himself,” one user wrote on Twitter in a reply. “Not a person worth any sympathy.”

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