I see three main indications related to Judas' state of mind in Matthew.
First, Matthew tells us that Jesus emphasized the importance of renouncing worldly goods and giving to the poor.
You received without paying, give without pay.Take no gold, nor
silver, nor copper in your belts, no bag for your journey, nor two
tunics, nor sandals, nor a staff; for the laborer deserves his food.
Later, in the story of the Rich Young Man:
Jesus said to him, “If you would be perfect, go, sell what you possess
and give to the poor, and you will have treasure in heaven; and come,
follow me.” (Matthew 19:21)
Why this Waste?
In chapter 19, however, it apparently seems to the disciples, especially Judas, that Jesus does not practice what he preaches on this issue:
Now when Jesus was at Bethany in the house of Simon the leper, a woman
came up to him with an alabaster flask of very expensive ointment, and
she poured it on his head, as he sat at table. But when the disciples
saw it, they were indignant, saying, “Why this waste? For this
ointment might have been sold for a large sum, and given to the poor.”
...Then one of the twelve, who was called Judas Iscariot, went to the
chief priests and said, “What will you give me if I deliver him to
you?” And they paid him thirty pieces of silver. And from that moment
he sought an opportunity to betray him. (Mt. 26:6:13)
So Matthew tells us the disciples collectively objected to the supposed waste of money that could have helped the poor, but in Judas' case he was particularly offended by it. This resulted in his decision to sell out Jesus and betray him.
The Last Supper
Matthew provides further information on Judas' state of mind when, at the Last Supper, Jesus declares "Woe unto him by whom the Son of Man is betrayed." Judas alone asks "Lord, is it I?" (26:24-25) Judas proceeds with his plan to betray Jesus, but Matthew has hinted that he is already plagued with a guilty conscience.
Putting these hints together without speculation beyond the text, I conclude that Matthew's account tells us Judas' original motivation was based on a feeling that Jesus hypocritically used worldly goods in contradiction to his teaching of apostolic poverty. This led him to betray Jesus, but once his former master had been condemned to death Judas felt remorse because he did not mean to bring a capital charge against Jesus. If we stick to Matthew's account alone, this is probably what accounted for Judas' remorse over betraying "innocent blood."
Addendum: information from other accounts
Luke 22:3-4 tells us that prior to the Last Supper, "Satan entered into Judas called Iscariot, who was of the number of the twelve; he went away and conferred with the chief priests and officers how he might betray him to them." We can speculate that after Jesus was condemned, Satan left Judas, leaving him conscience-stricken with deep remorse. However, Luke does not mention this, and his report in Acts indicates that Judas kept the money and used it to buy land. (see below)
In John 12 we are told that is was not that Judas cared for the poor but "because he was a thief, and as he had the money box he used to take what was put into it." This makes greed his motivation, as opposed to Matthew's implication that he was offended by Jesus' hypocrisy related to the teaching of apostolic poverty.
John 13:2 agrees with Luke that it was "the devil [who] had already put it into the heart of Judas Iscariot, Simon’s son, to betray him." Once again we can speculate that if the devil left Judas eventually, he would return to his normal state and thus feel remorse for betraying Jesus.
Acts 1:11 says that, rather than returning the blood money to the Temple, Judas "bought a field with the reward of his wickedness; and falling headlong he burst open in the middle and all his bowels gushed out." Although some interpret this to mean that Judas fell into the field after hanging himself, the fact that he used the money to buy the field calls into question whether felt remorse after learning that Jesus had been condemned.