PHOENIX -- The lead investigator in an Arizona sheriff's investigation into President Obama's birth certificate is selling his report as a book.

Retired detective and volunteer Maricopa County Sheriff's Posse member Mike Zullo is listed as the co-author of "A Question of Eligibility," an e-book for sale through Amazon and Barnes and Noble.

Arpaio unveils Obama birth-certificate probe

The book is a copy of the investigation findings presented to the press Thursday.

Zullo's co-author is Jerome Corsi, a well-known political conspiracy writer.

Phoenix television station KTVK reports (http://bit.ly/ykO9vU) Corsi denied using Sheriff Joe Arpaio, the self-proclaimed toughest sheriff in the country, as a promotional tool to sell his books and theories. Corsi supplied much of the research for the Sheriff's Office investigation.

Arpaio said at a news conference Thursday that his volunteer investigator found probable cause that the president's birth certificate is fake. Obama's campaign spokesman Ben LaBolt offered a light-hearted dismissal of Arpaio's probe, tweeting a link to a snippet from the TV series "The X-Files."