The late ISIS commander in Afghanistan and his heir apparent have more in common than their Taliban pasts and a tendency for jihad: both were former Guantanamo Bay detainees.
The death of commander Abdul Rauf this week — and apparent installation of Abdul Qayyum Zakir in his place — has cast an uncomfortable spotlight on the issue of former Guantanamo detainees rejoining the fight against the U.S.
Rauf — a former Taliban commander who was also known as "Khadim" and nicknamed "Mullah of one leg" — had spent "several years" in Guantanamo Bay, acccording to Afghan officials. After his release, he resumed activities with the Taliban but defected to ISIS prior to being killed on Monday.
Three senior members of the Afghan Taliban confirmed to NBC News that Zakir — described as a "seasoned commander" by one — was appointed Rauf's successor. All three spoke on condition of anonymity.
Zakir was reportedly a junior commander within the Taliban and arrested following the U.S.-led invasion. He was arrested in 2002 and transferred to Guantanamo before being released from the prison in 2007 — at which point he rejoined the Taliban and rose rapidly through its ranks. However, he had a falling out with the organization early last year and was relieved of his duties, according to Afghan and Taliban officials.
The mere existence of Guantanamo has been the subject of fiery debate between Republicans and the Obama administration for years — as has the risk of former detainees rejoining the fight once they are released.
President Barack Obama has called for a stepped-up push to shutter the detention center. There were 242 detainees in Guantanamo when Obama took office in 2009. Today, 122 are being held.
U.S. officials stress that the rates of former prisoners re-engaging in terror-related activities are low — and falling — and that stringent measures are in place to monitor former detainees for any signs they might rejoin the fight. That has done little to appease some Republican senators, three of whom last month introduced legislation to restrict the transfers of detainees.
Sen. John McCain, who was part of that group, said last week that 30 percent of former Guantanamo detainees are "either known to, or suspected to have returned" to the battlefields from which they came.
"What signal does this send to our young men and women in uniform, who may feel that they are left with an unsettling choice: whether killing our enemies is preferable to detaining them, watching them released, and having to face them another day on the battlefield?" McCain told a hearing on Guantanamo and the future of U.S. detention policy.
He drew that figure by adding together "confirmed" and "suspected" rates of re-engagement from data released by the Office for the Director of National Intelligence, which regularly publishes reports on the rate of recidivism. The most recent report was released in September 2014 and covers the period up through July 15, 2014.
Of the 620 detainees transferred out of Guantanamo as of then, 107 — or 17.3 percent — are confirmed to have re-engaged, according to the figures. An additional 77 former prisoners were "suspected" of re-engagement.
According to principal deputy under secretary of defense for policy Brian McKeon, 48 of the 107 ex-detainees confirmed of re-engaging are either dead or in custody.
"We take the possibility of re-engagement very seriously," he told the Senate Armed Service Committee last week, calling it a "primary concern" regarding any potential detainee transfers.
McKeon — and others in the Obama administration — have been quick to point out a decrease in re-engagement since the president took office in 2009.
"The rate of re-engagement has been much lower for those transferred since 2009," McKeon said. "This… speaks to the result of the careful scrutiny given to each transfer."
When asked if the U.S. was worried about rates of recidivism amid reports of Rauf's death, State Department spokeswoman Jen Psaki said Monday that while the number of confirmed detainees who re-engaged before Obama took office was 19 percent, that has dropped to 6.8 percent since 2009.
"The statistics on recidivism are pretty clear," Psaki told a briefing.
Obama administration officials have said that once a detainee is transferred from Guantanamo, the intelligence community continuously monitors for any signs or indications of re-engagement.
Those efforts were "updated" last month, according to the White House, after U.S. officials said that at least one of five Taliban militants released from Guantanamo in a controversial exchange for American soldier Bowe Bergdahl had "attempted to re-establish contacts" with the Taliban in Afghanistan.
White House Press Secretary Josh Earnest stressed that none of the individuals had returned to the battlefield, but said that mitigation and monitoring efforts "have been updated" to reflect concerns over possible recidivism.
"We continue to have confidence that there are measures in place to substantially mitigate the threat that they pose to American national security," Earnest said at the time.
"As we transfer prisoners from the prison, we need to make sure that we have measures in place to mitigate the risk that those individuals pose to the United States. And in the case of these five individuals, that’s exactly what we have," Earnest added.
Wells Dixon, a senior attorney at the Center for Constitutional Rights who represents current and former detainees, said the Obama administration has done “a very good job” of managing "what little risk there might be" from transferring detainees out of Guantanamo.
ISIS also has seized on the propaganda value of Guantanamo, Dixon noted. All of the group’s grisly videos of hostage beheadings and an immolation have shown captives dressed in orange jumpsuits — jumpsuits synonymous with the prison in recent years.
“If you are concerned about mitigating the threat from ISIS you should do everything that you can to close Guantanamo because one thing we do know for sure is that Guantanamo serves as a propaganda windfall for ISIS,” he added.
Cassandra Vinograd reported from London. Mushtaq Yusufzai reported from Peshawar, Pakistan. NBC News' Fazul Rahim contributed to this report.