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The acting head of Immigration and Customs Enforcement—who oversees the nation's second-largest federal investigative agency—may not be eligible for the permanent position under laws set up to keep politics out of the agency, according to one former high-level employee.

When John Sandweg, a former Arizona criminal defense attorney and associate of outgoing Department of Homeland Security Secretary Janet Napolitano, was named acting director of ICE, several critics questioned his credentials. Some told FoxNews.com his appointment seemed to be political, and others said the agency needed a leader who had come up through the ranks.

“Given that there are literally dozens of people within ICE who have more experience in management/law enforcement and meet these qualifications, there is no excuse for placing Mr. Sandweg as acting director of ICE,” said Anthony Ho, who was assistant special agent in charge of ICE’s San Francisco division before retiring in December.

Ho noted that the 2002 law which established the agency, then known as Bureau of Border Security, explicitly requires that the director “shall have a minimum of 5 years professional experience in law enforcement, and a minimum of 5 years of management experience.” The law was designed specifically to prevent the agency from becoming politicized, Ho said.

It was not clear if the same requirements apply to an acting director, but one source told FoxNews.com it was likely the intent that they would, otherwise an acting director could be installed indefinitely simply to get around them.

Sandweg, 38, was a fundraiser for Napolitano while she was governor of Arizona and came to Washington with her in 2009 when she was named DHS secretary. FoxNews.com has previously reported Sandweg’s extensive experience in political activism—a background recently raised by the House Homeland Committee, which wrote to President Obama expressing its concern with Sandweg’s appointment.

Sandweg has not been nominated for the permanent post, which would then require Senate confirmation. But even if his time at DHS were to count as law enforcement experience, which critics would dispute, he would still fall short of the five-year requirement.

“He doesn't even meet this minimal requirement set forth by Congress and certainly none of his professional experience meets any reasonable definition of law enforcement,” Ho told FoxNews.com.

The Bureau of Border Security was renamed the Bureau of Immigration and Customs Enforcement in 2003 and took on its current title, U.S. Immigration and Customs Enforcement in 2007.

The full 2002 law outlining the five year law enforcement and managerial experience requirement for the head of ICE is currently posted on the website of the Department of Homeland Security. Those same requirements for assistant secretary of ICE are listed in a March 16, 2010 “Statutory Qualifications for Executive Branch” prepared for members and committees of congress by the Congressional Research Service.

That would appear to indicate that the law did not change when the agency went through its various renaming.

A DHS official cited Sandweg’s work as general counsel for the department as providing experience for his current post. Sandweg helped craft border security and immigration enforcement strategies, helped remove more than 950,000 convicted criminal aliens since 2009, worked with the Pentagon to deploy the National Guard to the Southwest Border, the official said.

The White House did not immediately respond to a request for comment.

Similar concerns were raised when the Bush administration chose Julie Myers to head ICE in 2005 despite criticism of her credentials. She became head of the agency in a recess appointment.

Ho isn’t the first to raise concerns about Sandweg’s appointment appearing to support claims of the agency’s politicization. Earlier this month, FoxNews.com reported on his previous work defending killers and pedophiles and opposition to the appointment from lawmakers.

Rep. John Carter, R-Texas, who chairs the House Homeland Security Appropriations Subcommittee, was the first lawmaker to publicly blast Sandweg’s promotion to top post, calling him “in no way qualified” and his appointment the latest example of the “blatant politicization” of the nation’s second largest federal investigative agency.

"I am deeply disappointed by this appointment and believe it is disrespectful to the thousands of dedicated professionals at ICE who are working tirelessly to enforce our laws and provide for our security," he said following the announcement of Sandweg’s appointment.

"I urge the administration to re-think this appointment and promptly appoint a qualified, confirmable applicant for this essential post."

DHS officials continue to support Sandweg, and recently retired head of Customs and Border Patrol David Aguilar told FoxNews.com he is more than capable of running the agency.

“I think he’s extremely qualified to serve as the acting director of ICE and that’s in my opinion, that’s the opinion of a 35-year cop,” said recently retired Deputy Commissioner of Customs and Border Patrol, David Aguilar, who worked with Sandweg on immigration and border-related issues over the last few years.

But a growing chorus of lawmakers disagrees.  House Committee on Homeland Security Chairman Michael McCaul, R- Texas, and Rep. Jeff Duncan, R-S.C., who chairs the committee’s Oversight and Management Efficiency Subcommittee, wrote a letter to President Obama last week expressing "extreme concern" over Sandweg’s installation as acting ICE director. They noted his “critically thin” law enforcement experience.

"Despite extensive political experience, Mr. Sandweg's qualifications are critically thin in one area: experience in law enforcement," they wrote.

“Such a critical agency to our homeland security demands a leader with proven experience, significant managerial acumen, and tested judgment,” the congressmen wrote. “We fear your choice may possess none of these crucial qualities.”

The lawmakers asked Obama to respond to several questions pertaining to Sandweg’s background and qualifications and vetting for the acting director post. They have not heard back.

Their letter to the president came days after FoxNews.com published a detailed account of Sandweg’s career history, which includes his time as a criminal defense attorney representing sex offenders and murders in Arizona while he served as a major fundraiser for then governor Napolitano.

“A litany of concerning allegations has been raised against Mr. Sandweg,” reads their letter. “Perhaps the most concerning is the clear political partisanship displayed throughout his career.”

Email Jana Winter at jana.winter@foxnews.com