There's been a spate of "mass killings" recently. Quotation marks because of a couple of remarks on just those words. I just wrote a bit on a female student who killed two of her peers before killing herself. I find it difficult to call this a mass killing, she took out two -possibly predetermined- people. that's a murder suicide, but comes nowhere near the deathcount of Cho's rampage at Vtech, or McVeighs bombing in Oklahoma.
I don't mean to say that these events weren't serious or not horrible; there is probably a much more profound personal element at play which makes this casse something entirely different than a "kill as many unknown stragers as possible" scenario.
Likewise, I don't think that a robber who kills people resisting during his crime, or killing potential witnesses can be filed under the same label as Robert Hawkins, who killed eight people unknown to him in hopes of gaining immortal notiority.
These are both most horrible events, and I will make no attempt to judge either one as being worse yet than the other, I just mean to say that the words "mass killing" are being tossed around too much these days.