#3
Using the Laphystiinae key in Artigas, Papavero & Costa (1997), this fly does not cleanly key out to any genus. It looks like it has two flagellomeres, which apparently rules out Psilocurus (although the overall appearance is similar). Macahyba and Martinomyia are known from Peru, but the former lacks pulvilli so is ruled out. It looks like r1 may be open, but if it is closed than Martinomyia may be an option. Unfortunately I have hardly any photos of Neotropical Laphystiini, so my knowledge of the gestalt of these genera is limited.
Perhaps send this robber to Eric Fisher and see what he says.