Matthew 2.19-20: 19 But when Herod died, behold, an angel of the Lord appears in a dream to Joseph in Egypt, and said, 20 “Get up, take the Child and His mother, and go into the land of Israel; for those who sought the Child’s life are dead.”
Herod dies (singular), but the angel reports that those who sought the child's life are dead (plural). What is the angel talking about? Who are these other dead people alongside Herod? Well, probably no one, since the line is simply an echo from the Exodus narrative:
Exodus 4.19: 19 Now Yahweh said to Moses in Midian, “Go back to Egypt, for all the men who were seeking your life are dead.”
The correspondence is tight:
Exodus: τεθνήκασιν γὰρ πάντες οἱ ζητοῦντές σου τὴν ψυχήν.
Matthew: τεθνήκασιν γὰρ οἱ ζητοῦντες τὴν ψυχὴν τοῦ παιδίου.
Matthew: τεθνήκασιν γὰρ οἱ ζητοῦντες τὴν ψυχὴν τοῦ παιδίου.
In Exodus we have reason to believe that there may be men besides Pharaoh who want him dead ("surely the matter has become known," 2,14), and there are two chapters between the death of Pharaoh (2.23) and the assurance that "all the men" who have been wanting Moses dead are themselves now dead (4.19). In Matthew we find none of this: Herod dies (singular), and it is therefore announced that people (plural) are dead. I think these are the kinds of clues to look for to determine direction of influence between texts.
Ben.