The man Dallas police believe is responsible for murdering a 15-year-old boy in Deep Ellum is in custody. Shamar Anderson, 19, is charged with capital murder. Investigators say he opened fire on a group of people on Elm Street in Deep Ellum on August 28.Four victims were treated for non-life threatening injuries but a 15-year-old was critically hurt and died at the hospital. Dallas police have not released a motive for the shooting.RELATED:  Advertisement…The man Dallas police believe is responsible for murdering a 15-year-old boy in Deep Ellum is in custody. Shamar Anderson, 19, is charged with capital murder. Investigators say he opened fire on a group of people on Elm Street in Deep Ellum on August 28.Four victims were treated for non-life threatening injuries but a 15-year-old was critically hurt and died at the hospital. Dallas police have not released a motive for the shooting.RELATED:  AdvertisementWW…