A top Republican senator called Monday for an “immediate hearing” to investigate the controversial release of five Taliban prisoners in exchange for American Sgt. Bowe Bergdahl’s freedom, as he and others raised alarm that the administration just freed the “Taliban Dream Team.”

New questions are surfacing about the terms of the deal, as details emerge about the Guantanamo Bay prisoners sent to Qatar in exchange for Bergdahl – who was a Taliban captive in Afghanistan for the past five years.

Sen. Lindsey Graham, R-S.C., sent a letter to the leaders of the Senate Armed Services Committee calling for a hearing. He said the prisoners “have American blood on their hands and surely as night follows day they will return to the fight.”

Sen. John McCain, R-Ariz., on Sunday called the five former detainees “the hardest of the hard-core” and “the highest high-risk people,” who are “possibly responsible for the deaths of thousands.” In the interview on CBS’ “Face the Nation,” he noted others that have been released have “gone back into the fight.”

So who are these terror leaders the U.S. helped put back in circulation, and just how dangerous are they?

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Experts tell Fox News the men served in various military and intelligence roles linked to Al Qaeda before being sent to the U.S. detention center in Guantanamo Bay, Cuba.

The Joint Task Force Guantanamo classified all five as “high” risk to the U.S. Two of the five men are “wanted” by the United Nations on war crimes for the deaths of thousands of Shiite Muslims in Afghanistan.

The Taliban has long pushed for the release of the men who have been called the “GITMO Five” – a group of experienced jihadists who helped run the terror organization’s operations in pre-9/11 Afghanistan.

Here’s a closer look at the five Taliban commanders released in exchange for Bergdahl:

Abdul Haq Wasiq

Thought to be in his early 40s, Wasiq served as the Taliban deputy minister of intelligence and “had direct access to Taliban and Hezb-e-Islami Gulbuddin leadership,” according to an internal memo that assessed risk at Guantanamo. He reportedly used his office to support Al Qaeda “and to assist Taliban personnel elude capture.” He also reportedly arranged for Al Qaeda personnel to train Taliban intelligence staff. Wasiq belongs to the Khogyani Tribe and began his religious training under his father, Muhammad Saleem, who died in 1981.Three years later, he went to study Islam at Warah, a school located on the Afghanistan-Pakistan border near the Khyber Pass. When the Taliban assumed control in Afghanistan, a number of Islamic students, including Wasiq, went to Kabul. Wasiq has been accused by Human Rights Watch of mass killings and torture. According to a report by the Joint Task Force Guantanamo, Wasiq “arranged for Al Qaeda personnel to train Taliban intelligence staff in intelligence methods.”

Mullah Norullah Noori

As a senior Taliban military commander, Noori has been described in government reports as a military mastermind of sorts who engaged in hostilities “against U.S. and Coalition forces in Zabul Province.” Noori, who is estimated to be around 46 or 47 years old, has developed close ties to Taliban leader Mullah Omar and other senior Taliban officials, according to a JTF-GTMO report. Noori, who was named as the Taliban governor for the Balkh and Lagman provinces, is wanted by the United Nations for war crimes including the murder and torture of thousands of Shiite Muslims. Noori has been able to remain a “significant figure” to Taliban supporters and sympathizers. According to government records, which are based on conversations with Noori, he grew up in Shajoy where he learned to read and write at a mosque in his village. His father was the imam at the mosque. As a boy, he worked as a farmer on his father’s land. In March 1999, he traveled to Kabul where he met with Mullah Yunis, the commander of the Taliban security base, and expressed interest in joining the Taliban. After the Taliban front lines fell in November 2001, Noori traveled to Konduz where he was trained and worked with Omar. Noori has been implicated in the murder of thousands of Shiites in northern Afghanistan. When asked about the killings, Noori “did not express any regret and stated they did what they needed to do in their struggle to establish their ‘ideal state.’”

Mullah Mohammad Fazi

As the Taliban’s former deputy defense minister, Fazi was held at Guantanamo after being identified as an enemy combatant by the United States. Fazi is an admitted senior commander who served as chief of staff of the Taliban Army and as a commander of its 22nd Division. He’s also wanted by the United Nations on war crimes for the murder of thousands of Shiite Muslims in Afghanistan. According to documents, Fazi “wielded considerable influence throughout the northern region of Afghanistan and his influence continued after his capture.” The Taliban has used Fazi’s capture as a recruiting tool. “If released, detainee would likely rejoin the Taliban and establish ties” with other terrorist groups, the Guantanamo report says.

Mullah Khairullah Khairkhwa

Khairkhwa is the former governor of the Herat province and has close ties with Usama bin Laden and Mullah Omar. According to the Joint Task Force Guantanamo file, Khairkhwa “represented the Taliban during meetings with Iranian officials seeking to support hostilities against US and coalition forces.” Khairkhwa and his deputies are suspected of being associated with an extremist military training camp run by the Al Qaeda commander Abu Musab al Zarqawi, who was killed in 2006. U.S. authorities have also accused Khairkhwa of becoming a powerful opium trafficker.

Mohammad Nabi Omari

As a senior Taliban leader, Nabi Omari has held multiple leadership roles in various terror-related groups. Pre-9/11, Nabi, who is estimated to be in his mid-40s, worked border security for the Taliban – a position that gave him “access to senior Taliban commander and leader of the Haqqani Network, Jalaluddin Haqqani,” according to the JTF-GTMO report. Born in the Khowst Province of Afghanistan, Nabi Omari and his family were forced to resettle as refugees though In Miram Shah, Pakistan after the Soviet Union’s occupation in Afghanistan. In the late 1980s, Nabi Omari returned to Afghanistan where he fought with the mujahideen against the Soviets. During the early 1990s, he ping-ponged between Taliban-related positions and others, including a stint as a used car salesman. In August 2002, Nabi reportedly helped two al Qaeda operatives smuggle missiles in Pakistan. The weapons were smuggled in pieces and the plan was to reassemble the missiles once all of the pieces had been brought across. Nabi was caught in September 2002 and eventually moved to Guantanamo.