On the date of the accident, October 31, 2006, Catsouras and her parents ate lunch together at the family home in Ladera Ranch. After lunch, her father, Christos Catsouras, left for work while her mother remained at home. Around 10 minutes later, her mother heard a door shut along with footsteps out the back door. As she walked toward the garage, she was able to see her daughter reversing out of the driveway in her father's Porsche 911 Carrera — a car she was not allowed to drive. Her mother called her father, who began driving around trying to find his daughter. While doing so, he called 9-1-1 for assistance, apparently minutes before the accident, and was put on hold. When he was taken off hold, the dispatcher informed him of the accident. Catsouras was traveling on the 241 Toll Road in Lake Forest at approximately 1:38 pm, when she clipped a Honda Civic that she was attempting to pass on the right at over 100 miles per hour (160 km/h). The Porsche crossed the road's broad median, which lacks a physical barrier on that segment, and crashed into an unmanned concrete toll booth near the Alton Parkway interchange. The Porsche was destroyed, and Catsouras was killed on impact. Toxicological tests revealed traces of cocaine in Catsouras' body, but no alcohol.
Since Katya was sitting on a couch at the time of her death, this indicates that the stock of the Shotgun was rested against the floor, and the gun was fired vertically from underneath her chin, at a roughly 70-80 degree angle. Also, the presence of stellate patterning underneath her chin indicates that the muzzle of the gun was in very close contact with her chin when the gun was fired.
Despite the awkward positioning, it's extremely likely that Denis held the gun and pulled the trigger, as Katya had mentioned in an earlier livestream that she couldn't reach nor bring herself to pull the trigger; before asking Denis to do it for her. Bearing this in mind, it's worth noting that the Shotgun was likely not reversed; ie, the trigger guard was likely facing Katya, and not Denis.
Once the trigger was pulled, Katya's facial bones and the upper right portion of her head were largely obliterated, splattering brain matter on the couch and wall behind her, with more being sent for short distances in multiple directions throughout the room. During this event, the majority of her brain fell from her skull; hitting the edge of her seat before falling to the floor and breaking into two halves beside her feet. At this time she began to slump to her right, where she finally rested while blood pooled from her head.
Denis then stood up, took a step backward, and positioned the gun underneath his chin; now holding the gun reversed (with the trigger guard still facing toward Katya), his left hand gripping the middle of the barrel, and his right hand placed around the trigger guard.
As his eyes were very likely closed during the duration of their suicides, and he was holding the Shotgun in the air by one hand, the accuracy and stability of his aim was very poor. Upon pulling the trigger, the muzzle of the Shotgun was inches from his chin and pointed slightly toward the front of his face; as indicated by the presence of burnt gunpowder residue underneath and on his chin, a small/nonspaced entry wound underneath his chin, and the lack of stellate patterning.
Upon pulling the trigger, the projectiles entered underneath his chin, pierced the front right portion of the roof of his mouth, and exited approximately through his right cheekbone; completely destroying the area surrounding said cheekbone, his right eye; and shredding his frontal lobe, but leaving the rest of his head largely intact on the surface. At the moment of death, the recoil of the Shotgun ejected it from his hands, and he immdediately dropped to the floor, landing on his back.