A former U.S. Marine who became a Muslim radical, gang leader and bodyguard to the blind sheik behind the 1993 World Trade Center bombing is so adept at turning fellow prisoners into potential extreme jihadists that Florida prison officials have kept him in shackles and in solitary confinement for the last three years, and federal authorities want a judge to tack on another three decades.

Marcus Dwayne Robertson, a Muslim extremist also known as Imam Abu Taubah who once led a murderous New York gang dubbed “Ali Baba and the Forty Thieves” before resurfacing decades later as a radical imam at a Florida mosque, has been held at the John E. Polk Correctional Facility in Seminole County, Fla. Currently imprisoned on a weapons conviction, he faces sentencing on June 26 for a tax fraud conviction. Federal authorities want him locked up and kept away from other inmates out of fear he will turn them into dangerous jihadists, as he converted a number of fellow inmates including a white supremacist.

“The United States believes that the defendant is still an extremist, just as he was in the early 1990s,” prosecutors said in recent court filings in which they alleged Robertson continues to be a terrorism threat. “The only differences are that the defendant is now focused on training others to commit violent acts as opposed to committing them himself, and the violent acts are to occur overseas instead of inside the United States.”

Robertson, 46, who served time in the 1990s for crimes related to his days as a Brooklyn gang leader, has been imprisoned in Florida in 2011 on a gun charge. In just one year behind bars and among the general population, he allegedly radicalized 36 fellow inmates. Prison officials moved the persuasive imam into solitary confinement in 2012, where he has remained since. He faces sentencing later this month on a tax fraud conviction that prosecutors hope will keep him in prison for more than three decades. The U.S. attorney is using the Foreign Intelligence Surveillance Act to seek an enhanced sentence for Robertson.

Robertson’s attorney wants his client, who has been held for four years, released immediately with time served, but federal authorities are believed to fear that, if freed, Robertson could use his Orlando-area mosque to convince more young Muslims to go overseas and take up arms against the west.

“He is good at selling the dream,” said one of Robertson’s former colleagues.

Robertson has been held in a windowless cell in an otherwise empty wing of the prison facility and kept shackled to the floor with an armed guard assigned exclusively to him around the clock, according to a federal civil rights lawsuit he filed against the government pro se in 2012 that was ultimately dismissed. A person familiar with Robertson's case confirmed the conditions and told FoxNews.com prison officials fear Robertson’s military skills, which include special operations training, make him a threat to escape.

A prison spokeswoman told FoxNews.com that Robertson was put in solitary confinement “for his own protection” and is now held there by his own choice. But the tight security around Robertson extends outside the prison, with at least a 7-car armed caravan of federal marshals escorting him to his court appearances. Robertson’s attorney said his client believes he was put in solitary confinement in retaliation for filing a federal lawsuit against the government.

“Marcus Robertson has never tried to radicalize anyone,” said Robertson’s attorney Daniel Brodersen, who believes his client should be released immediately. “He’s tried to practice his religion in prison to the best of his ability.”

Over the last 30 years, Robertson has traveled a bizarre path that has seen him serve in the U.S. military, lead a murderous New York gang, consort with top Al Qaeda associates, go undercover for the FBI in Egypt, Africa and the U.S., and ultimately end up in a federal lockup facing more than 30 years in prison. Those who know him say Robertson became disenchanted while in the military, where he claims to have served in the elite counter-terrorism unit Joint Special Operations Command before leaving the service as a conscientious objector.

National Archives records confirm Robertson’s service from May 16, 1986 to May 1994, in the U.S. Marine Corps 2nd Force Reconnaissance Company as a field radio operator, but records indicate he was released from active duty in March 1990, discharged in the rank of corporal with training in radiotelegraph, scuba diving, marksmanship, parachuting, terrorism counteraction, surveillance, infantry patrolling and finance.

In early 1991, Robertson joined with other former Muslim security guards to form a robbery gang they called the ‘Forty Thieves’ with Robertson as the leader known as "Ali Baba."

They robbed more than 10 banks, private homes and post offices at gunpoint, shot three police officers, and attacked one cop after he was injured by a homemade pipe bomb.

Robertson also served as a bodyguard to Omar Abdel Rahman, nicknamed the “Blind Sheik,” who was part of the extremist Islamic group accused of the 1993 bombing of the World Trade Center. Government records claim Robertson donated more than $300,000 in stolen funds to mosques he attended.

After he was arrested in 1991 along with most of the other members of the Forty Thieves gang, Robertson cut a deal with prosecutors, serving just four years in prison while others remain behind bars.

Part of the pact involved Robertson going undercover for the FBI to document terrorists’ plans and networks in Africa, Egypt and the United States.

According to a source familiar with Robertson’s history, Robertson was thrown out of the program in Feb. 8, 2007 after he attacked his CIA handler in Africa.

Robertson quickly reinvented himself, founding the Orlando-based Fundamental Islamic Knowledge Seminary in 2008 and taking his Muslim name. He traveled the world, teaching at universities, including some in the United States. Videos of his lectures show him preaching against gays, “devil worshipers,” non-Muslims and such American pop culture icons as cartoon SpongeBob SquarePants, who he says is “gay.”

Under Islamic law, the Brooklyn-born Robertson married two women, Zulaika and Itisha Wills. Between them, and children he fathered outside these marriages, Robertson has 15 children. Through his teachings, videos and social media, he recruited an extensive network of followers in Florida and New York, an estimated 150 who reportedly are a concern for federal law enforcement.

Robertson was arrested on a firearms charge in 2011 and pleaded guilty in January, 2012. Just two months later, federal authorities charged him in with conspiring to defraud the IRS. Through wiretaps, the federal government documented interactions between Robertson and one of his student, Jonathan Paul Jimenez, who Robertson allegedly instructed to file false tax returns to obtain a tax refund to pay for travel to Mauritania, Northwest Africa, for study and violent jihadist training.

Jimenez, who reportedly knew Robertson for 11 years and, by his own admission, trained with the imam for a year in preparation for his travel to Mauritania, where he would study and further his training in killing, suicide bombing, and identifying and murdering U.S. military personnel, pleaded guilty Aug. 28, 2012, to making a false statement to a federal agency in a matter involving international terrorism and conspiring to defraud the IRS, and was sentenced April 18, 2013, to 10 years in federal prison.

While Robertson has been awaiting sentencing in the tax fraud charge, prosecutors have built a case against him for enhanced sentencing, alleging he’s involved with terrorism activities.

Robertson denies sending Jimenez overseas "to commit violent jihad.”

“The prosecution is attempting to characterize me as a ‘Teacher of Terrorists.’ … They are attempting to twist my statements to fit into a terrorist plot," he said in a statement that appeared on his website. In reality, they know I am not a terrorist teacher.”