Tabb was arrested while attending summer school at Harker Heights High School in Killeen, Texas.
The first suspect arrested earlier is a juvenile and prosecutors Monday were still considering what additional charges the two will face, possibly including murder, attempted murder and aggravated assault.
An investigation is ongoing into which of the two opened fire in the shooting or whether they both fired weapons.
The shooting took place at Austin's popular Sixth Street entertainment district at around 1:24 a.m. Saturday amid what police described as pre-pandemic crowds.
Douglas John Kantor, 25, died after the shooting and police said a total of 14 people were injured.