Michael Zullo, the investigator who took center stage at Arpaio's news conference last week, has already co-authored an e-book about his investigation and is selling it for $9.99 on Amazon and Barnes & Noble.
The book gives Zullo a financial motive to continue stoking the flames of a conspiracy theory that has been debunked numerous times by an array of independent investigations.
On Thursday, Arpaio and Zullo took to a podium in Phoenix to declare that after six months of investigating they believe the president's birth certificate is a computer-generated forgery.
In doing so, they joined the ranks of a fringe group of writers and activists who generally believe Obama is ineligible to be president because they doubt he was truly born in the United States.
The pair stopped short of saying they believe the president is illegitimate, but Arpaio said repeatedly that the investigation is "not over."
A day before the grand announcement, Zullo's e-book quietly went up for sale online. It was first spotted on Friday by a journalist for Phoenix television station KTVK.
Zullo wouldn't be the first person to have an eyebrow-raising event benefit their book sales. In January, Arizona Gov. Jan Brewer (R) turned a tarmac confrontation with President Obama into big time book sales, with her "Scorpions For Breakfast" skyrocketing on Amazon's best seller list.
Zullo's book was co-authored by Jerome Corsi, a writer for the conservative website WorldNetDaily who has been hawking the notion of a phony birth certificate for years. Corsi published his own book last year called "Where's the Birth Certificate? The Case that Barack Obama is not Eligible to be President."
Corsi also took part in last week's news conference and said he fed information and documents to investigators.
He told the Phoenix TV station that he and Zullo are splitting the profits from the new book, which is similarly titled "A Question of Eligibility: A Law Enforcement Investigation into Barack Obama's Birth Certificate and His Eligibility to be President." Neither Arpaio nor the sheriff's office would be making any money from the book, he said.
"Since he's a volunteer, Mike owns his work product and as such, he's permitted to utilize that work product for compensation," Corsi told the news station.
The sheriff has said the investigation was being conducted by his volunteer "Cold Case Posse" and its expenses were paid for by private donations, without any money coming from taxpayers.
But more recently, Arpaio said he is considering handing the investigation to some of his office's detectives, who are funded by taxpayers, because the volunteers found what he described as "probable cause" to believe a crime was committed in the creation of the birth certificate.
Zullo could not be reached for comment. A sheriff's spokesman told TPM on Monday that Arpaio knew a book was in the works and he was OK with it.
"The Sheriff does not believe that it will cloud the investigation and that the facts will speak for themselves," spokesman Jeff Sprong wrote in an email.
On Sunday, an opinion piece carrying the sheriff's name was printed in the Arizona Republic. Arpaio complained that the "biased media" had belittled his probe.
"They were practically salivating at the opportunity to embarrass me, my highly capable group of volunteer investigators and literally anyone else who would dare show an interest in the possibility that this investigation could lead to any real credible evidence into what they claim has already been 'looked into' or 'widely debunked,'" the piece said.
Arpaio wanted the media to look at the details he, Zullo and Corsi laid out during their lengthy news conference.
The sheriff did not mention, however, that much of their investigation was centered on a theory — involving "white halos" and "layers" from a digital scan of the birth certificate — that was already investigated and proven to be false by the conservative National Review Online before his own inquiry even began.