The FBI identified the shooter, who is dead, as Thomas Matthew Crooks of Bethel Park, Pennsylvania. A motive was not clear.
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Bethel Park is a predominantly white, relatively well-to-do city in the southern reaches of greater Pittsburgh. The site of the rally, Butler, is about an hour’s drive north of Pittsburgh.
Pennsylvania voter records listed a Thomas Matthew Crooks with the same address and birth date as a registered Republican, though it was not clear from the records when that was put in place.
This is important to know, but at the same time, the majority of registered members in both parties in Pennsylvania voted for the front-runner, and given his youth (20), the primary was his first election involving presidential candidates.
We need to wait until the facts about him come out. Very little is currently known beyond the party registration and the YouTube gun channel.