Herod, still seeking the infant John, sends officers to his father Zacharias. They demand to know where his son is, and he tells them that seeing as how he's been at the temple all the time, serving the Lord, he has no idea where his son is at the moment.
The officers return to Herod and report this. He is enraged (some more) because he believes that John is the one who will be king over Israel.
Herod sends the officers back to Zacharias demanding that he tell the truth and give up his son or be killed.
The officers obey, and Zacharias replies: "I am a martyr of God if my blood is spilled, for the Lord will receive my spirit; but you shed innocent blood at the entrance of the temple of the Lord." And the officers murdered Zacharias around dawn, but no one else knew what had happened. So he was deep inside the temple building, I assume.