Acts 1:21-26

21Wherefore of these men which have companied with us all the time that the Lord Jesus went in and out among us, 22Beginning from the baptism of John, unto that same day that he was taken up from us, must one be ordained to be a witness with us of his resurrection. 23And they appointed two, Joseph called Barsabas, who was surnamed Justus, and Matthias. 24And they prayed, and said, Thou, Lord, which knowest the hearts of all men, show whether of these two thou hast chosen, 25That he may take part of this ministry and apostleship, from which Judas by transgression fell, that he might go to his own place. 26And they gave forth their lots; and the lot fell upon Matthias; and he was numbered with the eleven apostles.

Comment: Here Luke records the replacement of Judas the traitor. Note the qualification for the replacement was that one be a witness of Jesus' ministry from the beginning to end and, most particularly, a witness of Jesus' resurrection from the dead. This passage indicates there were at least two other witnesses, and names them; Joseph and Matthias. To go through a process of nomination typically indicates the group had to be more than just a few to have sufficient candidates to choose from. 1 Corinthians 15:6 indicates there were at least 500. To have such large numbers of witnesses undermines any conspiracy. Further discounting conspiracy, Luke names the candidates thus opening their witness to scrutiny. Finally casting lots to see which candidate should replace Judas certainly removes any bias which might be present if any of the candidates were "insiders". In other words, the apostles didn't choose their pals to be other apostles. These were people with a variety of personalities and, in other scriptures, we see conflicts among them. If there was a conspiracy, surely the diversity of personalities would have exposed it long ago. Perhaps Jesus specifically chose a variety of personalities to insure a credible unbiased witness after his departure. Such a diverse group wouldn't be able to get the story straight even if they did try to cook up a story. In fact, one of them turned out to be a traitor. Surely he could've blown the cover if Jesus were a fake.