John Lightfoot on Matthew 14:10

[He beheaded John.] Josephus relates that John was imprisoned by Herod in Machaerus: Through the suspicion of Herod he was sent prisoner to Machaerus. Now Machaerus was the utmost bounds of Perea: and Perea was within Herod's jurisdiction. But now if John lay prisoner there, when the decree went out against his life, the executioner must have gone a long journey, and which could scarcely be performed in two days from Tiberias, where the tyrant's court was, to execute that bloody command. So that that horrid dish, the head of the venerable prophet, could not be presented to the maid but some days after the celebration of his birthday.

The time of his beheading we find out by those words of the evangelist John, "but now the Passover was nigh," by reasoning after this manner: It may be concluded, without all controversy, that the disciples, as soon as they heard of the death of their master, and buried him, betook themselves to Christ, relating his slaughter, and giving him caution by that example to take care of his own safety. He hearing of it passeth over into the desert of Bethsaida, and there he miraculously feeds five thousand men, when the Passover was now at hand, as John relates, mentioning that story with the rest of the evangelists. Therefore we suppose the beheading of the Baptist was a little before the Passover, when he had now been in durance half a year, as he had freely preached by the space of half a year before his imprisonment.