It didn't have to.

If we look at the text of the Nicene Creed which was written in 381 at the Second Ecumenical Council in Constantinople which was ordered convened by Emperor Theodosius himself, there was no need to apologize or excuse Romes behavior. The key part of the creed is thus:

and suffered and rose again in fulfillment of the Scriptures

Numerous references in the Old Testament refer to "blood sacrifice" such as Leviticus 17:11

because the life of the flesh is in the blood itself, and I myself have given it to you all so that atonement may be made for your souls on the altar, since the blood itself makes atonement through the life that is in it.

We often neglect to recognize the elements of the Bible that refer to practices that we find out of joint with our modern understanding of Christianity and even Judaism, but in the 1st Century A.D., many of these practices were still in place, including ritual sacrifice. Many may know of the story in the Bible where Jesus overturns the tables of the money changers. What was happening was merchants were overcharging and swindling those who were purchasing animals and making tithes in the temple which were meant for literal sacrifice. This is important to understand as it plays a key role in the understanding of the meaning of the Crucifixion. Jesus's death, was a symbolic blood sacrifice to wash away the sins of the world, and is even mentioned as part of the New Testament in Hebrews 9:22 as well as Jesus' own reference during The Last Supper in Mark 14:24-25

“This is my blood of the[a] covenant, which is poured out for many,” he said to them. “Truly I tell you, I will not drink again from the fruit of the vine until that day when I drink it new in the kingdom of God.”

Even by Jesus' own words the wine symbolized his blood being sacrificed in order to establish the New Covenant, or new compact between man and God, which was foretold in the Old Testament in the book of Jeremiah.

In Christian theology, Jesus who is seen as God as Man, sacrificed himself manifest as his own son, (Trinity doctrine is a whole other thing) to wash away the sins of mankind. We can get into more complex theological arguments, part of which was involved in the very first Ecumenical councils, major schisms, and conflicts within the Church, but it ties back into the sentiment established by what Jesus refers to in that passage from Mark in that he will not drink of the vine until he drinks it in "the kingdom of God," which is when Jesus returns to judge the living and the dead and establish Gods Kindom on Earth. In the most basic terms Jesus had to die in order to save mankind. This is where Pontius Pilate comes in.

Pilate, as the governor of Judea, had Jesus brought before him and directly questioned Jesus about a key factor "Are you the king of the Jews?" For Pilate, a man who had no joy in governing a territory of the Roman Empire that was regularly in turmoil and revolt (in fact over the next 200 years several revolts by the Jews against Rome occured), he wanted no part in the religion conflicts of the Jewish people. If Pilate killed Jesus, and Jesus was indeed a respected leader and revolutionary, he feared an uprising, and simply didn't want the trouble. So when Pilate asked Jesus if he claimed to be King of the Jews Jesus replied "You say I am", to which Pilate said, "I find no crimes committed." He meant to at least the authority of Rome, so he had absolutely no problem with Jesus. Jesus was like John the Baptist and other wandering prophets of 1st Century Judea, practically a commonality. We know of several people who claimed themselves or were claimed to be the Messiah such as Athronges, Judas son of Hezekiah, Simon of Peraea, Judas the Galilean, "The Samaritan Prophet" (A direct contemporary of Jesus). The common factor to all of these men is that they were all rebels that attacked either Roman authorities or their Judean puppet kings. So when Pilate found Jesus to not be a violent rebel, he saw Jesus as merely another wandering preacher and no concern of his.

However, as the Jewish authorities continued to be angered by his lack of punishment of Jesus, and the mob they had assembled at the public trial were on the border of a riot, he according to the tale in Mark, literally washed his hands and said, "I am innocent of this man's blood." Yes, as Governor his duty was to carry out the punishment of death the crowd demanded, so he had his men crucify Jesus, in fulfilment of the promises of the Old and New Testament, including Jesus' own words.

So in a literal, legal sense, The Roman state was not responsible for the death of Jesus as it was the people of Jerusalem and the Jewish authorities who chose to sentence him to death. In the literary/religious sense, Pilate and Rome were a tool of God. Jesus chose to go to his death, including willingly turning himself into authorities when they came for him in the Garden, ordered his own disciples to not defend him (even reattaching the ear of one of the authorities that had been cut off by one of them)

Now, having said that, we can get into all sorts of theological debates over some of the finer points of the scripture and metaphysics and moral philosophies involved, but we don't have the time or space to rehash what was basically the first five hundred years of Christian theology. Just understand that when it comes down to the point. Rome had nothing to apologize for in the philosophical sense or the legal sense as his crucifixion was the will of God himself.