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Is there a serial bomber in Austin, Texas?

The city experienced its fourth bombing in 17 days on Sunday evening. The bomb injured two men in their twenties, and city police have asked the bomber to reach out and reveal his demands. Last night’s victims are expected to live, but the bombings have claimed two lives already: Draylen Mason, 17, and Anthony Stephan House, 39, died after package bombs were delivered to their homes. Mason’s grandmother was also injured, and a fourth person, Esperanza Herrara, was injured in a separate blast.

Mason and House are black, fueling speculation that the bombings could be the work of white supremacists. The Washington Post reports:

The first two bombs killed black people—a 39-year-old construction worker and a 17-year-old high school student—related to prominent members of Austin’s African American community who were also close personal friends. The third bomb seriously injured a 75-year-old Hispanic woman, but it was addressed to a different home and apparently exploded when she was carrying it, according to two people familiar with the case.

Last night’s victims, however, are white. Police say the bomb that injured them had been placed by the side of the road, then triggered by a tripwire. It’s not certain, then, that Sunday’s bomb is linked to previous bombings, or that the injured men were even the bomb’s intended targets, but police are operating under the assumptions that all four bombs are linked until new information demonstrates otherwise.