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the only reliable "keys" to Lucilia are those of Dr. Rognes. Szpila is very reliable as well. I recommend Rognes or Szpila. The linked document is a summary of what Dr. Rognes already published.

genitalia should be used for an accurate id. The hypopygium is not visible in the photo here (neither are the cerci). You have the specimen? you can view the cerci?

the width of the frons in relation to the parafacials and the head are known to be different between the two species (caesar and illustris.) The legs are black on illustris versus black/brown of caesar. I cannot tell if they are brown in this photo.

My first instinct is caesar but it seems to be a little more bluish than I have seen before. I cannot rule out caesar but it still looks strange to me. I only have specimens sericata, caesar, ampullacea and silvarum. I am no different than anyone else with Lucilia in that a good guess depends upon the features visible. Do you have more photos?