Testifying in a Chicago court in the trial of his Pakistan-born friend Tahawwur Hussain Rana, Headley had less than a week ago said that he was no longer proud of the attack that 166 people dead and over 300 injured.
But as lawyers of Rana, the co-accused in the attack and facing the trial, made efforts to prove their client's innocence and establish that Headley was falsely implicating him, a taped conversation between Headley and his wife was presented in the court.
As recently as a few months ago, Headley had apparently called his wife and said, "Once I am out, I can write a book and make a movie on this and we can make a lot of money. Once I am out we can do religious work."
He also said if he was ever released from prison, he would like to "fix" misconceptions the media and the public has about Islam.
In another conversation, he had apparently told one of his wives that he "a made a fool" of Rana and repeatedly took advantage of since they first met in 1974.
"I acknowledge that I made a fool of him. He should be released. Poor fellow is stuck for no reason. It was my fault," Headley had allegedly said.
When Rana's attorney Patrick Blegen confronted him with the telling statements, Headley -- the federal prosecutors' star witness against Rana -- clarified that he meant he duped Rana by "using him" and "getting him to assist."
It was with Rana's blessing that Headley set up a phony Indian office, using his immigration business name, so that he could scout targets and gather information for the Lashkar-e-Taiba (LeT) in preparation for the 60-hour siege in Mumbai, according to prosecutors.
Headley has already plead guilty in the case and is now testifying against other co-accused after striking a deal with the prosecutors of not being meted out a death penalty or extradition. He has revealed the role of Pakistani state services in attack.
However, with the new disclosures, his credibility could take a hit in the eyes of the jury and pose a serious threat to the prosecution of those guilty.
When the trial resumes on Wednesday, Headley is likely to cough up more on the nexus between terrorist outfits al Qaeda, LeT and Pakistani intelligence agency ISI during is cross-questioning on the 19th floor of the Dirksen Federal Courthouse.
Headley has already pleaded guilty of his crime, while Rana refused to own up the charges of supporting terrorism.
The trial is expected to be over by June 15.
If convicted, Rana may face a life sentence.