This is a super difficult one which falls into one of those murky areas of the family that I don't like to delve into. Resembles something in the tribe Minthoini, I was thinking close to Sumpigaster. But there's quite a few possible genera from various tribes which resemble this overall shape. Would be interesting to get a dorsal view with the wing in focus, but I guess that this wont be possible.
I don't think this is Trigonospila, but I can't really explain why, other than gestalt. The thickened gena at the mid-eye level appears to be distinctive, and I'll try to see how this matches up in the collection. Anyway, I would recommend leaving this at Tachinidae sp. for the time being.