Tatum, of Fort Worth, was in a crowd outside an Austin club when the driver smashed his car through a street barricade and into the festivalgoers.
Austin resident Jamie West, 27, and Dutchman Steven Craenmehr, 35, were killed at the scene. Sandy Le, 26, died of her injuries March 17.
More than 20 others were injured.
Police have identified the driver of the vehicle as Rashad Owens, 21. He is charged with capital murder and aggravated assault with a motor vehicle, and prosecutors are expected to seek additional charges against him from a grand jury. He's accused of driving drunk and fleeing from police, then intentionally driving into the festival crowd.
The aspiring rapper from Killeen is jailed on a $3 million bond.
The South By Southwest festival attracts more than 200,000 people to Austin for a technology conference, film festival and thousands of music performances.
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