Robber flies are generally large, showy insects. They can be quite charismatic, in fact. One of my favorite web sites that discusses robber flies can be found on the Wisconsin Butterflies site.
Cerotainia albipilosa is quite small and perhaps not so showy.
Still, it can be sort of satisfying to see a fly kill another type of fly that we might not care for so much.
The prey seems to be some kind of midge.