A.T. Robertson Commentary Matthew 2:20

"Arise and take the young child and his mother, and go into the land of Israel: for they are dead that sought the young child`s life." — Matthew 2:20 (ASV)

For they are dead (τεθνηκασιν). Only Herod had sought to kill the young child, but it is a general statement of a particular fact as is common with people who say: "They say." The idiom may be suggested by Ex 4:19 "For all are dead that sought thy life."