• The Pentagon said it has transferred a Moroccan citizen from Guantanamo Bay to his home country, marking the first such release under President Biden.
• Biden has vowed to shut down the Cuban prison facility, which was established after the 9/11 terrorist attacks.
• The transfer of Abdullatif Nasser to Morocco leaves 39 inmates left at the island prison off Cuba's eastern coast.

The Pentagon said Monday it has transferred a Moroccan citizen from Guantanamo Bay to his home country, the first such release under President Joe Biden, who has vowed to shut down the prison facility.

The transfer of Abdullatif Nasser to Morocco leaves 39 inmates left at the island prison located off Cuba's eastern coast. His transfer follows a panel decision in 2016 that found the alleged former al-Qaeda member no longer needed to be detained by the U.S. to protect American national security.

Nasser's lawyer cheered his transfer.

"This is an enormously welcome event. I'm still in shock about it," attorney Shelby Sullivan-Bennis said in a brief interview by phone.

The release of Nasser, who is in his mid-50s, reflects the ping-ponging of presidential policy on Guantanamo Bay.

President George W. Bush established the detention facility in 2002, in the wake of the Sept. 11, 2001, terrorist attacks. Nearly 800 individuals have at some point been imprisoned at the site.

As the prison camp gained a reputation for torture and other human rights abuses, former President Barack Obama tried to shut it down. Obama's failure to do so became one of his administration's most notable unfulfilled promises.

"I'm so happy that the promises of the Biden administration have come true, when those of the Obama administration did not," Sullivan-Bennis said.

Obama's successor, former President Donald Trump, reversed the government's Obama-era stance and issued an executive order to keep Guantanamo open. Only one prisoner was transferred under Trump.

Nasser, whose name is also transliterated as Abdul Latif Nasir, was imprisoned at Guantanamo since 2002. While a government panel known as the Periodic Review Board recommended in 2016 that he be transferred to Morocco subject to certain assurances about security and humane treatment, the process could not be completed under Obama, the Pentagon said.

The Pentagon did not say whether Nasser will be detained in Morocco. He was not immediately available to comment through his attorney. The Associated Press reported that after his arrival in Morocco, police took him into custody and said they would investigate him on suspicion of committing terrorist acts — even though he was never charged while in Guantanamo.

Sullivan-Bennis said it was her understanding that her client was held briefly in Morocco and then allowed to go home within an hour.

"In time for Eid, amazingly," she said in a written message, referring to the Muslim religious holiday that began Monday evening.

"The United States commends the Kingdom of Morocco for its long-time partnership in securing both countries' national security interests," the Defense Department said in a statement. "The United States is also extremely grateful for the Kingdom's willingness to support ongoing U.S. efforts to close the Guantanamo Bay Detention Facility."

The Justice Department declined to comment.

—The Associated Press contributed to this report.

Correction: An earlier version misstated Trump's view of Guantanamo in one reference.

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