John Chrysostom — as excerpted in the Catena Aurea on Luke 9:7-9

“(ubi sup.) When Herod then heard of the miracles which Jesus was performing, he says, John have I beheaded, which was not an expression of boasting, but by way of allaying his fears, and bringing his distracted soul to recollect that he had killed. And because he had beheaded John, he adds, but who is this.”