I went ahead and sent this shot to a robberfly expert and this is what he had to say. Based on the comments below, I will move this to Holcocephala fusca and do understand that it is no a 100% ID but the 2 species are almost identical.

I believe that your nice photo is of Holcocephala fusca Bromley. However, this is not a positive identification - as fusca is very similar to abdominalis (they are functionally a pair of cryptic species). H. fusca was described (in a very short, two sentence paragraph!) as being distinct from abdominalis by having a general darker color. It was soon treated as a synonym of abdominalis and essentially forgotten. Recent observations show that individuals with the darker 'fusca' coloration also have more slender antennae and legs (1st flagellomere of antenna of abdominalis distinctly broader in middle - with a spindle-shape; fusca has a more elongate, parallel-sided flagellomere 1; hind tibia & basitarsis of abdominalis about 35% broader than hind femur, while only about 15% broader in fusca); and a slightly different aedeagus shape. So, now I am tentatively treating them as distinct spp.

Eric M. Fisher, Ph.D.
Senior Insect Biosystematist
Calif. Dept. of Food & Agriculture

Thanks!