Aileen Pizarro, 43, and her daughter Aryana (12) died on the scene of the imapct.
According to the Daily Mail, police reports show that the 18-year-old Heitmann, who was known in the gaming community as "OG McSkillet", was speeding in his McLaren on Thursday afternoon, driving in the wrong direction on I-805 HOV, where he crashed into the Hyundai SUV driven by marriage and family therapist Aileen Pizarro.
A spokesperson for California Highway Patrol said: "At this point I don't have anything to clarify why or what possible made him do what he did, whether he was under the influence at the time, whether he was having any other issues".
McSkillet's channel had close to 900,000 subscribers, and he'd posted a video there showing off his black McLaren in December.
An 18-year-old gamer who had hundreds of thousands of YouTube subscribers was killed Thursday after he was involved in a head-on collision at more than 100 miles per hour that also killed two others.
Muslims celebrate Eid Al-Adha, the Feast of the Sacrifice
In the Christian and Jewish version of the event, Prophet Ibrahim is ordered to kill his other son, Prophet Isaac (Ishaq). Fasting the day before the holiday washes away two years worth of sins in the previous and coming years.
In one video, from December 2017, Heitmann discussed his vehicle, a 641-horsepower black McLaren 650S, which he said "beats just about every other super auto in a drag race".
The crash caused a chain reaction between five cars and one other person was injured. He was later known for trading "skins", which are digital files used to customize the appearance of the game's players.
Witnesses say the driver then got out of the vehicle, smashed a window at the school, before driving off again.
"Yesterday, both my mother and sister were taken from our family in an instantaneous auto accident in San Diego", the account writes.
Sanchez said CHP believes Heitmann was involved in an incident earlier in the day at a local elementary school.