According to the District Attorney's Office, the attack occurred in June 2020 at their residence on the 400 block of 16th Avenue in the city's Richmond District. Sun was reportedly in the middle of a Zoom class, and someone on the call "reported seeing the victim get knocked down and hit."
District Attorney Brooke Jenkins called the killing "horrific and brutal."
Guan has been in custody in the San Francisco County Jail since June 18, 2020.
He faces 25 years to life in prison and will be sentenced June 16.