@parados,
Mass killers in general or mass killers by firearms and as the bombers are less likely to committed suicide then the shooters and once more most shooters do not get into shootings contests with police the movie theater shooter just gave up for example.
In other word most of these shooters was not looking for shoot outs with other armed people.
Footnote the tops two mass US killers did not use firearms. One a nice big bomb and the other a few boxcutters.
Then the biggest killer of school children in school were a bomber not a shooter also.