From his recent book Josephus, Judea, and Christian Origins: Methods and Categories (amazon.com) (and thanks to Hendrickson Academic for the review copy!). In his article “Josephus as Authority for First Century Judea”, Mason works over the practice of attempting to discern/locate underlying sources used by Josephus:

Since Josephus’s literary art demonstrably involves changes of narrative voice, complexity of character development, calculated repetition of charged language, variation of diction, and diversionary excursus, it seems impossible to devise criteria based on such phenomena for extracting sources. Attempting such recovery would require a sort of literary Heimlich maneuver, performed on someone who has long since digested the item being sought. The result is likely to be neither appealing nor useful. (Mason 38)

Now that’s a great word picture! I just started reading the book, and the first essay (which the above quote comes from) is excellent. Looking forward to the balance of them.