This is John the Baptist - Ον εγω απεκεφαλισα, Whom I beheaded. These words are added here by the Codex Bezae and several others, by the Saxon, and five copies of the Itala. - See the power of conscience! He is miserable because he is guilty; being continually under the dominion of self-accusation, reproach, and remorse. No need for the Baptist now: conscience performs the office of ten thousand accusers! But, to complete the misery, a guilty conscience offers no relief from God - points out no salvation from sin.

He is risen from the dead - From this we may observe:

1. That the resurrection of the dead was a common opinion among the Jews; and

2. That the materiality of the soul made no part of Herod's creed.

Bad and profligate as he was, it was not deemed by him a thing impossible with God to raise the dead; and the spirit of the murdered Baptist had a permanent resurrection in his guilty conscience.

This.

Matthew 11:11 Truly I say to you, Among them that are born of women there has not risen a greater than John the Baptist...

Matthew 16:14 And they said, Some say that you are John the Baptist: some, Elias; and others, Jeremias, or one of the prophets.

Mark 8:28 And they answered, John the Baptist; but some say, Elias; and others, One of the prophets.

John 10:41 And many resorted to him, and said, John did no miracle: but all things that John spoke of this man were true.

do shew forth themselves in him. or, are wrought by him.

The Martyrdom of John
'At that time Herod the tetrarch heard of the fame of Jesus, 2. And said unto his servants, This is John the Baptist; he is risen from the dead; and therefore mighty works do shew forth themselves in him. 3. For Herod had laid hold on John, and bound him, and put him in prison for Herodias' sake, his brother Philip's wife. 4. For John said unto him, It is not lawful for thee to have her. 5. And when he would have put him to death, he feared the multitude, because they counted him as a prophet. 6. …
Alexander Maclaren—Expositions of Holy Scripture

First Withdrawal from Herod's Territory and Return.
(Spring, a.d. 29.) Subdivision B. Feeding the Five Thousand. ^A Matt. XIV. 13-21; ^B Mark VI. 33-44; ^C Luke IX. 11-17; ^D John VI. 2-14. ^c 11 But { ^a and} the multitudes heard thereof [heard of Jesus and his disciples crossing the lake], ^b 33 And they saw them going, and ^c perceiving it, ^b many knew them, ^d 2 And a great multitude followed him, because they beheld the signs which he did on them that were sick. ^b and they ran together there on foot from all the cities, and outwent them. ^a …
J. W. McGarvey—The Four-Fold Gospel

The Miraculous Feeding of the Five Thousand
In the circumstances described in the previous chapter, Jesus resolved at once to leave Capernaum; and this probably alike for the sake of His disciples, who needed rest; for that of the people, who might have attempted a rising after the murder of the Baptist; and temporarily to withdraw Himself and His followers from the power of Herod. For this purpose He chose the place outside the dominions of Antipas, nearest to Capernaum. This was Beth-Saida (the house of fishing,' Fisher-town,' [3198] as …
Alfred Edersheim—The Life and Times of Jesus the Messiah