HOUSTON, Texas (KTRK) -- An MS-13 gang member who authorities believe is responsible for two fatal shootings across the Houston area is now in custody.Douglas Alexander Herrera-Hernandez, 20, is charged with capital murder in Fort Bend and Harris counties.According to a Houston Police Department spokesperson, Herrera-Hernandez was arrested early Saturday in Arlington, Virginia.Herrera-Hernandez, also known as "Terror," murdered a 16-year-old at the Buffalo Run Park in Missouri City on June 13, investigators allege. They believe the 16-year-old had witnessed several gang-related murders and was working with authorities.Nearly a month later, Houston police identified Herrera-Hernandez in the fatal shooting of 26-year-old Kevin Alvarez. According to witnesses, Herrera-Hernandez and Alvarez had been arguing before the shooting.