According to CNN:
A reporter from the Tampa Bay Times reports the pilot was a Florida area postal worker seeking to protest campaign finance reform. The paper is reporting it called Secret Service and Capitol Hill police before he flew. The reporter who spoke before the flight has been tweeting from Washington as the postal worker landed.
The Capitol Police, however, have not disclosed his identity. They did say he is in custody for questioning and they’re seeking to find out whether the landing was due to a mechanical issue or some other issue.