Added line breaks because this was a real slog to get through without them.
Okay so, this is one of those 'broadly true but lacking context' statements. Deuteronomy 32:35 reads 'It is mine [God's] to avenge; I will repay. In due time their foot will slip; their day of disaster is near and their doom rushes upon them.' This is referenced again in Paul's writings in Romans 12, 17-21, which includes the wording 'leave room for God's wrath'. [New International Version, aka the first non-awful translation google begrudgingly spat out at me.]
Basically, God's followers were disallowed from committing acts of grievous violence, but not exclusively because doing so was morally wrong. Instead, God was the one who ultimately punished wrongdoers, and it was up to him to decide how that punishment would occur. Many times in the Hebrew scriptures, he directed the Jews to destroy and eradicate tribes who worshiped wicked gods like Baal, who demanded that infant children be burned alive on his altars to ensure good rainfall. Other times, he chose to destroy cities that were unusually wicked by his own hands, such as Sodom and Gomorrah. Yet other times, he maneuvered political entities such as the Babylonians to wage war against nations that had persecuted his people, such as the Assyrians.
As for the Jews who rejected Jesus and deliberately impaled the savior their own prophets had spent centuries preaching to them about, they were punished by the Romans in 70 CE, when Jerusalem was utterly destroyed and the hypocritical Jewish priesthood completely annihilated. The context is also important; Jesus was not asking forgiveness on behalf of the priesthood who condemned him. He was asking forgiveness for the Roman soldiers who were executing him. These men had no familiarity with Jewish traditions, prophecies or laws. They really didn't have any idea what they were doing, and even Pilate himself tried quite hard to get Jesus freed, only caving to the demands of the Jewish mob when they threatened to declare an open insurrection if he let Jesus go. Meanwhile, these was absolutely no forgiveness for the Priesthood class.
So, in conclusion, while God forbids killing directly, he does not withhold consequences for deliberate evildoing and does not expect wicked people to be let free with a slap on the wrist. Forgiveness can only be obtained after punishment is administered. Absolutely nowhere in the bible does it say that an 'I'm sorry' absolves a person from the legal repercussions of his actions.