Matthew 27 NIV
Judas Hangs Himself
1 Early in the morning, all the chief priests and the elders of the people made their plans how to have Jesus executed. 2 So they bound him, led him away and handed him over to Pilate the governor. 3 When Judas, who had betrayed him, saw that Jesus was condemned, he was seized with remorse and returned the thirty pieces of silver to the chief priests and the elders. 4 “I have sinned,” he said, “for I have betrayed innocent blood.” “What is that to us?” they replied. “That’s your responsibility.” 5 So Judas threw the money into the temple and left. Then he went away and hanged himself. 6 The chief priests picked up the coins and said, “It is against the law to put this into the treasury, since it is blood money.” 7 So they decided to use the money to buy the potter’s field as a burial place for foreigners. 8 That is why it has been called the Field of Blood to this day. 9 Then what was spoken by Jeremiah the prophet was fulfilled: “They took the thirty pieces of silver, the price set on him by the people of Israel, 10 and they used them to buy the potter’s field, as the Lord commanded me.”[a]
Jesus Before Pilate
11 Meanwhile Jesus stood before the governor, and the governor asked him, “Are you the king of the Jews?”
One is naturally inclined to believe that Judas killed himself just prior to the Lord's crucifixion, going by this text.
In 1 Corinthians 515:3-8, Paul states the following:
3 For what I received I passed on to you as of first importancea : that Christ died for our sins according to the Scriptures, 4 that he was buried, that he was raised on the third day according to the Scriptures, 5 and that he appeared to Cephas, and then to the Twelve. 6 After that, he appeared to more than five hundred of the brothers and sisters at the same time, most of whom are still living, though some have fallen asleep. 7 Then he appeared to James, then to all the apostles, 8and last of all he appeared to me also, as to one abnormally born.
(Note: "the Twelve" is not capitalized in every translation)
Thus, we see that Paul is saying that Jesus appeared to the twelve after His resurrection. But that cannot be, as Matthew, as shown above, indicates or insinuates that Judas killed himself prior to the crucifixion; therefore, being a witness to the risen Christ would be an impossibility.
So, was Judas still part of the group when Jesus began to appear publicly following His resurrection or not? Did he die before or after the crucifixion/death/resurrection or some other time?
