29 Woe unto you, scribes and Pharisees, hypocrites! Because ye build the tombs of the prophets and garnish the sepulchers of the righteous,
30 and say, ‘If we had been in the days of our fathers, we would not have been partakers with them in the blood of the prophets.’
31 Therefore ye are witnesses against yourselves, that ye are the children of them that killed the prophets."
Please explain how the Pharisees build of the tombs, demonstrate that they are like those who killed the prophets. As that what is said here; that the very act of building the tombs show that. because of the use of the word therefore.
The commentaries that I have read so far does not answer the question. Most of them say that the Pharisees witnesses against themselves by later killing Jesus.