PHOENIX >> America’s self-proclaimed toughest sheriff finds himself entangled these days in his own thorny legal troubles: a federal grand jury probe over alleged abuse of power, Justice Department accusations of racial profiling and revelations that his department didn’t adequately investigate hundreds of Arizona sex-crime cases.

Rather than seek cover, though, Maricopa County Sheriff Joe Arpaio is seeking to grab the spotlight in the same unorthodox fashion that has helped boost his career as a nationally known lawman.

Arpaio on Thursday unveiled preliminary results of an investigation, conducted by members of his volunteer cold-case posse, into the authenticity of President Barack Obama’s birth certificate, a controversy that has been widely debunked but which remains alive in the eyes of some conservatives.

At a news conference, Arpaio said the probe revealed that there was probable cause to believe Obama’s long-form birth certificate released by the White House in April is a computer-generated forgery. He also said the selective service card completed by Obama in 1980 in Hawaii also was most likely a forgery.

"We don’t know who the perpetrators are of these documents," Arpaio said, although he said he doesn’t think the president forged the documents.

Earlier, the 79-year-old Republican sheriff defended his need to spearhead such an investigation after nearly 250 people connected to an Arizona tea party group requested one last summer.

"I’m not going after Obama," said Arpaio, who has criticized the president’s administration for cutting off his federal immigration powers and conducting a civil rights investigation of his office. "I’m just doing my job."

Some critics suggest Arpaio’s aim is to divert attention from his own legal troubles while raising his political profile as he seeks a sixth term this year. The sheriff vehemently denies such strategies are in play.

"You say I need this to get elected? Are you kidding me? I’ve been elected five times. I don’t need this," he said in a recent interview.

Democratic state Sen. Steve Gallardo said Arpaio is pandering to relentless critics of the president.

"It doesn’t matter what President Obama does, they’ll never support him," Gallardo said. "It’s those folks who will continue to write checks to Sheriff Joe because of this stuff."

Arpaio’s probe comes amid a federal grand jury investigation into the sheriff’s office on criminal abuse-of-power allegations since at least December 2009, focusing on the sheriff’s anti-public corruption squad. Separately, the U.S. Justice Department has accused Arpaio’s office of racially profiling Latinos, basing immigration enforcement on racially charged citizen complaints and punishing Hispanic jail inmates for speaking Spanish. Arpaio denies the allegations and said the investigation is politically motivated.

Critics also have sought Arpaio’s resignation for more than 400 sex-crimes cases over a three-year period ending in 2007 that were either inadequately investigated or weren’t investigated at all by the sheriff’s office after the crimes were reported. The sheriff’s office said the backlog was cleared up after the problem was brought to Arpaio’s attention.

Speculation about Obama’s birthplace has swirled among conservatives for years. "Birthers" maintain that Obama is ineligible to hold the country’s highest elected office because, they contend, he was born in Kenya, his father’s homeland. Some contend Obama’s birth certificate must be a fake.

Hawaii officials have repeatedly confirmed Obama’s citizenship, and Obama released a copy of his long-form birth certificate in April in an attempt to quell citizenship questions. Courts also have rebuffed lawsuits over the issue. Of late, the president’s re-election campaign has poked fun at it, selling coffee cups with a picture of the president’s birth record.

On Thursday, Obama’s campaign spokesman Ben LaBolt offered a light-hearted dismissal of Arpaio’s probe — he tweeted what he referred to as a "live link" to the sheriff’s news conference, but instead provided a link to a snippet of the old conspiracy-theory based TV series, "The X-Files."

Arpaio has said he took deliberate steps to avoid the appearance that his investigation is politically motivated. Instead of using taxpayer money, the sheriff farmed it out to lawyers and retired police officers who are volunteers in a posse that examines cold cases. Other posses assist deputies in duties that include providing free police protection at malls during the holiday season or transporting people to jail.

Even as he is under fire by the federal government, the sheriff remains popular among Republicans.

GOP presidential candidates have courted him for his endorsement throughout the primary season. At last week’s GOP presidential debate in Arizona, Arpaio won loud cheers. During a question about Arizona’s border woes, Pennsylvania Sen. Rick Santorum said the government ought to give local police agencies the chance to enforce immigration law as Arpaio has.

Bruce Merrill, a longtime pollster and senior research fellow at Arizona State University’s Morrison Institute for Public Policy, said the subject of the investigation plays to the sheriff’s base of supporters. And, he said, it highlights Arpaio’s gift for publicity.

"It’s something that the press will cover," Merrill said. "He’ll get a lot of exposure from it."