WASHINGTON — A Donald Trump supporter who, federal law enforcement officials, say plotted to kill FBI special agents investigating him on Jan. 6 charges appears to have been armed with a gun when he became the fourth rioter to breach the U.S. Capitol, federal prosecutors said at trial on Tuesday.

Edward Kelley, of Tennessee, is one of just a handful of Jan. 6 suspects who are still being held in pre-trial custody, meaning that they haven’t yet been convicted of a crime. Kelley was…