"As we suspect, it is a fraudulent document," Arpaio said. "My original intent was to clear the president of the United States."
Members of Maricopa County Sheriff Arpaio's posse said in March that there was probable cause that that the president's long-form birth certificate released by the White House in April 2011 was a computer-generated forgery.
According to the posse's chief investigator, Mike Zullo, numeric codes on certain parts of the birth certificate indicate that those parts weren't filled out, yet those sections asking for the race of President Obama's father and his field of work or study were completed.
President Obama's campaign declined to comment on Arpaio's allegations.
So-called "birthers" claim Mr. Obama is ineligible to be president because he was born in Kenya.
The Associated Press contributed to this report.