You did have the DC snipers, but the female answer I would guess is pretty straightforward: lower testosterone, lower levels of relevant drug treatment, plus a lower incidence of the typical forms of mental illness involved.
We are still a majority white country, so I’d think a majority white expectation might be expected. But I think above average intelligence seems to go with the profile for this sort of premeditated thing. We’re dealing with still quite low numbers for statistical averages overall, but just with one such shooter, I doubt that Asians would be or are underrepresented even though Asian men on average have a slightly lower average testosterone level.
>> I doubt that Asians would be or are underrepresented <<
Off the top of my head, I count two Asians: the Korean at Virginia Tech and Maj. Hasan at Ft. Hood. I wonder if there have been others?
In the meantime, with 10% of the USA being black, there ought to be ca. 10% blacks in the population of mass shooters. But I’m not aware of any.