Thanks!

One possibe scenario is that after the nestling died, it was initially attacked by adult flesh flies, at least one of which deposited an egg, which developed into a larvae, which then began consuming the tissue. At this point, the fly larvae or pupa was then attacked by the wasp, which laid it's own egg into one of these stages, and then emerged as this adult.

At least eight species of Brachymeria are known to attack Sarcophaga. Good work, John.