The United States sent Guantánamo’s youngest captive home to a prison in his native Canada on Saturday, ending the decade-long U.S. detention of the Muslim militant who grew from a teenager into adulthood at the Pentagon’s prison camps in Cuba.

In 2002, at age 15, Omar Khadr hurled a grenade in war-torn Afghanistan that killed an American soldier. He was captured and kept by U.S. forces ever since. Now 26, he’s home and could serve up to six more years in a Canadian prison. Or authorities could release him sooner. Canada considers him a juvenile offender who can apply for parole a year from now.

“He thinks he’s in a dream. He’s pinching himself,” said Toronto attorney John Norris, who spoke to Khadr soon after his arrival. “He never believed this day would come; he’s been betrayed so many times before.”

Khadr departed the base in Cuba before dawn Saturday, a secret transfer 10 days after a Canadian diplomat paid Khadr a visit on his 26th birthday. He landed at a Royal Canadian airbase in Ontario and was transferred to the Millhaven maximum security prison for what his lawyer described as an assessment of the most suitable place to serve out his sentence.

The case of Khadr — Guantánamo’s last Western captive — stirred debate in international law and human rights circles.

Because he was captured at such a young age, some called him a child soldier who was dropped off in the war zone by his father and deserving of rehabilitation not interrogation. Others called him the respected scion of an al Qaida family, nicknamed Canada’s First Family of Terror in news reports, and opposed his repatriation.

Psychiatrist Michael Welner, testifying at the Guantánamo war court for the prosecution and paid by the Pentagon, called Khadr a continuing danger who spent his time at the U.S. prison camps in Cuba “marinating in a community of hardened and belligerent radical Islamists.”

Khadr’s lawyers offered up tales of abusive treatment in U.S. custody. He’d been questioned in Afghanistan while emerging from surgical anesthesia, they argued. He was used as a “human mop” at Guantánamo after he urinated on himself and the floor during an interrogation. His lawyer was forbidden from seeing him during his first two years of interrogations.

U.S. troops captured Khadr, who was near death, in a July 27, 2002 firefight at a suspected al Qaida compound near Khost, Afghanistan.

U.S. air strikes had leveled the compound and as a Special Forces unit assaulted, Khadr admitted in a 2010 guilty plea, he threw a grenade from the rubble that mortally wounded Army Sgt. 1st Class Christopher Speer, 28. Medics were able to save Khadr’s life and turned him over to what became a decade of on-again off-again interrogation.

Since his conviction, he was confined to a maximum-security wing at Guantánamo, a mostly solitary existence that his lawyers tried to ameliorate with a Canadian-style college preparatory curriculum — literature, physics and videos of “Little Mosque on the Prairie,” a popular Canadian TV show about a Muslim community in a fictional prairie town.

He also read Shakespeare with his U.S. defense lawyer, Army Lt. Col. Jon Jackson, who played Juliet to Khadr’s Romeo.

“Now that Khadr is back in his own country, Canada should assist in his rehabilitation,” said Human Rights Watch counterterrorism counsel Andrea Prasow. “International law provides him the right as a former child soldier to be reintegrated into society.”

The nation’s Public Safety Minister, Vic Toews, took months to decide whether Khadr was entitled to repatriation.

“I am satisfied the Correctional Service of Canada can administer Omar Khadr’s sentence in a manner which recognizes the serious nature of the crimes that he has committed and ensure the safety of Canadians is protected during incarceration,” Toews said in a statement.

Defense lawyers had asked that he get special protections at whichever Canadian prison was chosen because of his notoriety.

In his plea agreement, Khadr also admitted to planting landmines in Afghanistan meant to shred invading allied forces. Once captured, and interrogated, he directed U.S. troops back to their location to safely disarm them.

Testimony at pre-trial hearings showed U.S. interrogators saw the 15-year-old as a human intelligence treasure trove because as a child his family had spent time with the family of Osama bin Laden in Afghanistan. His father, Ahmed Said killed in Pakistan in 2003, was seen in Canada as a high-level al Qaida functionary who moved his family to Pakistan and Afghanistan in the years before the Sept. 11, 2001, attacks.

One of Omar Khadr’s elder brothers, Abdurahman, also spent a short time in Guantánamo as an informant but never saw his kid brother there. Abdurahman is now free in Toronto.

With Saturday’s transfer, the Pentagon now has 166 captives at Guantánamo.

The youngest is now believed to be a Yemeni named Hassan bin Attash, whose leaked detention records indicate he was born in Yemen in 1985. He’s the younger brother of former CIA captive Walid bin Attash, an alleged al Qaida lieutenant now at Guantánamo facing charges in the Sept. 11 death penalty case.

The Khadr transfer could break a logjam in efforts to get other captives to plead guilty. Defense lawyers have characterized the Obama administration’s inability to get Khadr back to Canada as an obstacle to negotiations with other alleged al Qaida foot soldiers whose testimony might be useful at the Guantánamo war court.

Amnesty International USA used the occasion of the transfer to urge President Barack Obama to close the detention center. “Khadr’s tragic story underscores why Guantánamo should close — not tomorrow, but today,” Amnesty Executive Director Suzanne Nossel said in a statement.

“Given the Obama administration’s glacial pace towards closing the U.S. controlled detention center, little and late though it is,” she added, “today’s news represents progress.”