The defendant, who was 17 at the time of the killing last October, admitted to voluntary manslaughter and received the maximum sentence for that charge for a juvenile, five years in a secure youth treatment facility, according to the Los Angeles District Attorney's office.
The video in the media player above is from a previous report.
The case involving the other defendant, also 17 at the time, is still going through the legal system, with the next court date set in two weeks.
The names of the two juveniles have not been disclosed publicly.
2 teens arrested in downtown LA stabbing death
The store owner, Du Young Lee, 56, was fatally stabbed near the wig store he ran for almost two decades. Witnesses say two teens tried to steal a wig from the store but the owner chased and confronted them, leading to the stabbing.
Friends and family members say over the years the store owner was involved in multiple incidents involving confronting shoplifters, sometimes ending up injured but continuing to stand his ground. Other store owners described him as heroic, seeing his efforts as symbolically standing up for them as well.