The Gun Violence Archive, which began collecting data on gun violence in the U.S. in 2013 (here), (here), recorded more than 4,400 mass shootings in the last decade, Executive Director Mark Bryant told Reuters via email. Its definition of mass shooting is four or more people shot resulting in injury or death (excluding the perpetrator).
Of those, “the number of known suspects in mass shootings which are trans is under 10 for the last decade,” which translated to “1:880 [or 0.11%] of the 4,400 shootings” they recorded, he said.
Fact Check-Majority of US mass shooters are cis men, not transgender or non-binary people