A gunman opened fire from a rooftop onto a Dallas ICE facility, killing one detainee and critically wounding two others before taking his own life. Authorities say they are unsure what motivated the shooter, who used a rifle in the attack.

Authorities remain uncertain about the exact reason behind the Annunciation shooting, despite extensive evidence left by the attacker. What they have uncovered points to a troubling obsession with previous mass shooters, offering the only clear insight into a crime that remains shrouded in mystery.