Zechariah was the son of the great priest Jehoiada. Wicked Queen Athaliah ordered all the seed royal to be executed in order to eliminate any possible rival claimants to the throne of Judah. Jehoiada hid baby Joash from the murderers, and later made him king. Due to his extraordinary greatness, Jehoida the Priest was buried with honor in the tombs of the Kings.
Years later (2 CH 24:20-25) King Joash scorned Jehoiada’s kindness by murdering the priest’s son Zechariah, who as a prophet rebuked the king for embracing idolatry, “You have abandoned YHWH, He has abandoned you”. The king’s assassins killed the prophet in the Temple courtyard. As he died, he said, “May YHWH see and demand an account”. In a year, Jerusalem had been plundered, its leaders killed. King Joash, severely wounded in the attack, was assassinated by his servants, and denied burial in the tombs of the kings.
Jesus chose Abel and Zechariah as prime examples of the religious leaders persecuting the prophets (Luke 11:50) because they were the first and last martyrs in the Old Testament. Zechariah was not the last martyr time wise, but the last book in the Hebrew canon is 2 Chronicles. Thus, for Jesus to say Abel to Zechariah would be like us saying from first to last or Genesis to Revelation.