Gabbard was part of a 20-strong security team called the Threat Research and Analysis Group.
Wal-Mart made the case public last month and denied Gabbard's claims that his actions were the result of pressure from Kenneth Senser, a former senior CIA and FBI official who has headed Wal-Mart's office of global security since 2003.
Gabbard did not work for Senser's department, although the company and others familiar with the case said Senser has the authority to work with staff from other divisions in carrying out investigations. Gabbard has said he felt pressured by Senser to find information leaks, while Wal-Mart has denied that those conversations alleged by Gabbard took place.
Gabbard and his former supervisor, Jason Hamilton, who was also fired, have declined repeated requests for interviews with The Associated Press.
But in a text message to The Associated Press last week, Gabbard confirmed the allegations that he was part of a broader surveillance operation against company workers, critics, vendors and consultants that he alleged were approved by the company.