John Gill Commentary Acts 12:3

"And when he saw that it pleased the Jews, he proceeded to seize Peter also. And [those] were the days of unleavened bread." — Acts 12:3 (ASV)

And because he saw it pleased the Jews
That is, as Beza's ancient copy adds, "his stretching out his hands upon the faithful"; this pleased the Jews, a bloodthirsty generation of men, who had killed the prophets, and the Lord Jesus, and who were now greedy after the death of the apostles: it may easily be seen from what principle and spirit Herod acted; it was not out of regard to the Jewish religion, rites, and ceremonies, but to ingratiate himself into the affections of the people:

he proceeded further to take Peter also ;
a principal apostle, and who was well known, and against whom the Jews had doubtless a particular antipathy, and would have been glad to have been rid of him; this Herod was, sensible of, and therefore to please them, ordered him to be taken up:

then were the days of unleavened bread ;
or the feast of the passover.