Zacharias son of Barachias was slain by Zealots long after Jesus talked about it in Matthew 23 verse 35?

The assumption of the question is that Matthew was in error for reporting something which did not happen in the correct time frame. There are a number of significant problems firstly with the assumption that Matthew was in error and also that the other possible explanations are unsatisfactory.

Firstly, if Matthew was a contemporary of the events he describes, it is unlikely he would make such an error. Further in this same regard the contemporary critics of the Christian faith would also have had ample opportunity to correct the error yet there is no evidence whatsoever that this ever took place. Secondly, there are a number of possible explanations as to the identity of the relevant individual apart from the one who is chosen with the least likelihood of being the candidate, as mentioned in the paragraph immediately above.

The possible candidates include the following all with varying degrees of plausibility:

1.The father of John the Baptist was a priest and would not have been popular with the reigning Jewish authorities as the father of the one who so vehemently denounced them and called them a 'brood of vipers.' (Hardly a compliment)

2.The OT Prophet Zechariah. This actually is mentioned in Jewish tradition (that he was killed in the temple).

3.The Zechariah mentioned in 2 Chronicles is commonly regarded as a candidate.

4. A transmission error is considered a possibility when the Aramaic version of Matthew was transferred to the Greek.

5.The Zechariah in question is unknown.

Source: Article by J P Holding. see Related Links.

Summary:

Thus with a number of different possible explanations it is not necessary, in fact also for other reasons it is reasonable to assume that Matthew was not in error.

Another Answer:

Chronicles 24:20-21, And the spirit of God came upon Zechariah the son of Jehoiada .... And they conspired against him, and stoned him with stones at the commandment of the king in the court of the house of the lord.

This verse says that Zechariah was the son of Jehoiada, but Jesus said that Zechariah was the son of Barechiahs. Matthew 23:35.

Matthew 23:35 That upon you may come all the righteous blood shed upon the earth, from the blood of righteous Abel unto the blood of Zacharias son of Barachias, whom ye slew between the temple and the altar

If Matthew was referring to the temple destruction in 2 Chronicles, then surely he was in error.

If Matthew was referring to the destruction of the Temple in 69AD, then he is historically correct but chronologically wrong. This only proves that Matthew is narrating events in his Gospel that have already happened. Also proved that Matthew were written after the destruction of the Temple in 69AD.