This has led to some fun conspiracy-theory speculation - "Why do serial killers usually have only two names while 'lone gunmen' have three?" - but it is mostly the result of newspaper convention, e.g. "Police arrested Charles Francis Xavier of the 1400 block of Graymalkin Lane in North Salem, N.Y., on charges of operating an unlicensed daycare." Sometimes the middle name doesn't seem necessary - Leon Czolgosz doesn't usually get the "Frank," and Sirhan Sirhan is still just Sirhan Sirhan - but there are a lot of guys named "John Booth" out there, and police blotters traditionally have used full names and addresses to cut down on mistaken identity.
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