Complex sentence: The book's title allegedly comes from a news broadcast, heard by Burroughs, about a fire at a circus during which the announcer broke into hysterics on reading the line, very likely the Hartford Circus Fire, which took place on July 6,1944.
Split into simpler sentences: The book's title allegedly comes from a news broadcast, heard by Burroughs, about a fire at a circus during which the announcer broke into hysterics on reading the line. In fact, the reference almost certainly was to the Hartford Circus Fire, which took place on July 6,1944.