Four years after the Stonewall riots and the formation of the Metropolitan Community Church, an arson attack on a private gay pride gathering at the UpStairs Lounge bar in New Orleans killed 32 people in a horrifically painful way and injured about three dozen more people who were there on June 24, 1973. Per the linked material:
The UpStairs Lounge arson was the deadliest fire in New Orleans history and the largest massacre of gay people ever in the U.S.
The mostly likely perpetrator of the attack was never charged but committed suicide in 1974. Despite it's magnitude, this event is not widely known.