GUANTANAMO BAY NAVY BASE, Cuba — Toronto-born Omar Khadr, Guantanamo’s youngest and last Western detainee, pleaded guilty Monday to committing war crimes under a plea deal meant to send him home to Canada next year.

Khadr’s full admission is spelled out in a 50-paragraph statement that admits he was a murderer, al-Qaida conspirator and spy in Afghanistan in July 2002. He was 15.

To authenticate it, Army Col. Patrick Parrish spent less than an hour questioning Khadr, who hunched intently over the plea and agreement that would return him to Canada in a year to serve seven more years in prison there.

Captured near dead in a firefight in Afghanistan, he has grown to a bearded, strapping 6-foot-plus man behind the razor wire at Camp Delta.

In the agreement, according to two legal sources with direct knowledge, Khadr says he eagerly took part in a July 28, 2002 firefight with U.S. Special Forces in Afghanistan that mortally wounded Sgt. 1st Class Christopher Speer, 28, of Albuquerque, N.M.

Speer’s widow, Tabitha, wore a black dress to court and sat weeping when the portion about her husband’s murder was mentioned.

Sources say that, in the plea, Khadr also says that he had aspired as a teenager to kill Americans and Jews and described his father, Ahmed Said, as a part of Osama bin Laden’s inner circle, a trusted confidant and fundraiser.

Judge Parrish said the full text would be released today.

“Omar Khadr is not a victim. He’s not a child soldier,” said Navy Capt. John F. Murphy, the Pentagon’s chief military commissions prosecutor. “He’s convicted on his own words.”

Khadr’s plea spared him a risk of life in prison, had he been convicted at trial.

Under a deal sealed through an exchange of diplomatic notes Saturday, the United States will support a plan to transfer him to Canada at age 25 to serve the last seven years of an eight-year sentence.

Khadr’s Canadian lawyer cast his young client as a victim. “He had to come to a hellish decision,” said Dennis Edney, “and he had to make it on his own to get out of Guantanamo Bay.”