In matt 23, the scribes and pharisees are accused of murdering Abel, who was murdered by Cain, who did not even have any descendents that lived past the flood.... how great must have been their sin that God would even bring the retribution on them of this sin from the beginning of time....

and compare God's curse pronounced on Cain with what happened to the Jews after the destruction of the temple (emphasis mine):

Gen 4:10-15 And He said, “What have you done? The voice of your brother’s blood cries out to Me from the ground. So now you are cursed from the earth, which has opened its mouth to receive your brother’s blood from your hand. When you till the ground, it shall no longer yield its strength to you. A fugitive and a vagabond you shall be on the earth.”
And Cain said to the LORD, “My punishment is greater than I can bear! Surely You have driven me out this day from the face of the ground; I shall be hidden from Your face; I shall be a fugitive and a vagabond on the earth, and it will happen that anyone who finds me will kill me.”
And the LORD said to him, “Therefore, whoever kills Cain, vengeance shall be taken on him sevenfold.” And the LORD set a mark on Cain, lest anyone finding him should kill him.