This was not the deadliest mass shooting in US history.
http://www.theatlantic.com/news/archive/2016/06/orlando-deadliest-mass-shooting/487058/
For educating pro-gun control people this is a good example to share:
https://en.wikipedia.org/wiki/Happy_Land_fireThe Happy Land fire was an arson fire that killed 87 people trapped in an unlicensed social club named "Happy Land", at 1959 Southern Boulevard in the West Farms section of the Bronx in New York City on March 25, 1990.... The evening of the fire, González had argued with his former girlfriend, Lydia Feliciano, a coat check girl at the club, urging her to quit. She claimed that she had had enough of him and did not want anything to do with him anymore. González tried to fight his way back into the club but was ejected by the bouncer. He was heard to scream drunken threats in the process. González had recently lost his job at a lamp factory, was impoverished, and had virtually no companions.[citation needed] González returned to the establishment with a plastic container of gasoline. He spread the fuel on a staircase, the only access into the club, and then ignited the gasoline.
More people killed, a nightclub and it happened not long ago...