I met a guy named Sam Pate. He was a radio guy in Dallas in the 60s and was live on the air when it happened. He told me that the shooter escaped down the storm drain (they were much bigger then before the street was resurfaced), went through the tunnels under the city, and was on a plane to Chicago by the time Kennedy was pronounced dead. https://www.jfk.org/collections-archive/sam-pate-oral-history/