PHOENIX — Former Maricopa County Sheriff Joe Arpaio said Thursday that he planned to continue his investigation into former President Barack Obama’s birth certificate.

In an interview with the San Jose Mercury News before a speaking event in Fresno, Arpaio said the birth certificate “has to go down as the biggest cover-up in the history of the United States. Nobody wants to touch it.”

Arpaio has been investigating Obama’s birth certificate for years. In December, he said he had conclusive proof that the document was a forgery.

The former lawman was backed on the issue by President Donald Trump, though the latter changed his tune during the presidential campaign.

“President Barack Obama was born in the United States, period,” Trump said at a rally last September.

In the Mercury News interview, Arpaio pointed out that Trump never directly addressed the document’s authenticity. The lawman said has maintained that he doesn’t care where the president was born, just about the possible forgery.

Trump didn’t say what led to the switch of his opinion but he blamed his then-rival for the White House, Hillary Clinton, for starting the rumor during her failed 2008 Democratic presidential campaign.

Clinton’s campaign responded quickly. Former Manager Robby Mooks called Trump’s actions, “disgraceful.”

Arpaio’s so-called proof was primarily focused on the date stamps on the lower-left portion of the birth certificate, among other things.

Investigator and posse member Mike Zullo said the angle of the hand-stamped dates was identical to that of the 1995 birth certificate of Johanna Ah’Nee, the person whose birth certificate was used to create an alleged template for Obama’s document.

Zullo said two experts agreed that several parts of Ah’Nee’s birth certificate were used to forge Obama’s.

“This carries federal penalties,” Zullo said.

Zullo also said there were concerns with the security paper Hawaii uses, the raised seal on the document and the fact that it appears to be a computer document that has been printed and scanned at least one time.

“The document is unreliable and is inauthentic,” he said.

Arpaio has gone as far as to send a deputy and member of his volunteer posse to Hawaii to talk to officials. He was one of the nation’s leading voices on the debunked controversy, often referred to as birtherism, over Obama’s birthplace.

Arpaio was voted out of office in the November general election. He has claimed that a criminal contempt of court case against him — in which he was found guilty and pardoned by Trump — was a last-ditch attempt by the Obama administration to take him down.

The Associated Press contributed to this report.

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