She was a campaign volunteer.

The story was initially reported as fact in a paper owned by a major repuke.

Drudge had the story up before it was reported in any paper. He is usually informed of stories like this through the campaign.

McCain / Palin personally talked to the girl after the story broke.

There is about as much circumstantial evidence that points to the McCain campaign being involved in this hoax as there was that she originally made the story up in the first place.

Let's have an investigation of McCain campaign's involvement in this. Now that she confessed to the lie and has been charged and arrested for her crimes, the McCain campaign is now suspect in a criminal offense.

On edit: I also believe the fact that the McCain campaign had a press release ready to go on this and the fact that they ran with this story adds to the evidence that they were involved.