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.