If you believe that Christ was praying for ALL those killing Him, His enemies then you will would have to say that all crimes are forgiven, if you can nail the Son of God to a cross then surely all other sins are forgiven, but of course they are not, we know that there is not universal salvation, we know that not everybody will be in the kingdom, and Christ says about His enemies; "bring them before Me and slay them" Luke 19:27. We also know that as Christians when we sin, God just does not forgive and turn a blind eye, He punishes us, we don't get pardoned we get judged, we know there is a judgement to come as well, if all is forgiven, then there is no judgement, might as well say 'do as thou wilt for all is permissible', exept that would be the Satanic doctrine in a nutshell. So was the intercessory prayer of Jesus (Isaiah 53:12) was not universal, Jesus was not praying for the Pharisees whom had conspired the crucifixtion, so if the prayer is specific than it can be reconciled with Luke 19:27 and also with the 'unforgivable sin' and the Judgement Day when not all we recieve forgiveness, the prayer must be specific, He was not praying for all those present, some were there as believers they were lamenting, and some like the thief actually were convicted and converted during the Crucifixtion.
1. Cor 2:8 "Whom none of the princes of this world knew; for had they known it, they would not crucified the Lord of glory". Yet this cannot be extended to all those who had a hand in the death of Jesus, but only to the ignorant multitude, Jesus had told the Pharisees who He was, they were not ignorant, some did know, remember when Herod slaughtered the babies, Herod knew the Kiing had been born, he knew the prophecy so he sought to kill Jesus, he knew what he was doing, but Jesus' prayer was for those present that did not know what they were doing. We could imagine that many had know idea who Jesus was, they just thought it was another criminal being executed, they were not part of the conspiracy, they did not arrange His death, they were just there, not knowing, they can be forgiven, God knows their hearts and minds.
Among the ignorant multitude of Isarelites there were the elect and some already believers, there would have been dissent between those that knew Jesus and that He was the eternal Son of God, and those who had know idea who Jesus was, some of those would have later heard the gospel and converted. Acts 3:17 "And now, brethren, I wot that through ignorance ye did it, as did also your rulers, But those things, which God before had showed by the mouth of all his prophets, that Christ should suffer, He hath so fullfilled, repent therefore and be converted."
Here we have Peter in Acts explaining it to those very Israelites that were at the crucifixtion, and Peter calls the brethren and they are called to repent and be converted, and the Holy Spirit is present and this was done, they became Christian, 'those that parted His garments', those in their ignorance were forgiven by the Lord of Glory and they believed.