From the Liveleak description

Investigators are looking into an incident in Van Nuys, where a police
officer shot and killed a man who was holding a woman at knifepoint.
Coroner’s officials identified the man as 18-year-old Jeovany Mendoza of Van Nuys.

responded to a 911 call at about 8:30 p.m. Saturday near Saticoy Street
and Tobias Avenue. Once on the scene, officers found Mendoza holding
the knife to the woman’s throat. After Mendoza refused to drop
the weapon, police say one of the officers opened fire, killing him.
According to investigators, the woman may have suffered cuts to her
hands and throat, but was expected to be OK. Her identity was not
immediately released. No one else was seriously injured.

The circumstances surrounding the initial threat were not immediately known. The case remains under investigation.