A prisoner who begs to stay indefinitely at the Guantánamo Bay detention center rather than be sent back to Algeria probably has a strong reason to fear the welcoming reception at home.

Abdul Aziz Naji, who has been held at Guantánamo since 2002, told the Obama administration that he would be tortured if he was transferred to Algeria, by either the Algerian government or fundamentalist groups there. Though he offered to remain at the prison, the administration shipped him home last weekend and washed its hands of the man. Almost immediately upon arrival, he disappeared, and his family fears the worst.

It is an act of cruelty that seems to defy explanation.

Mr. Naji, 35 and born in Algeria, was picked up by the police in Pakistan in May 2002 and turned over to the Americans on suspicion of being a terrorist. He admitted working for the humanitarian wing of Lashkar-e-Taiba, the Pakistani terrorist organization, but the Bush administration never charged him with a crime, explained why he was being held, or demonstrated any connection to terrorist acts.

The Obama administration, which is trying to reduce the population at Guantánamo, battled Mr. Naji’s lawyers all the way to the Supreme Court for the right to send him to Algeria. Mr. Naji argued that once he was in his home country, he would be tortured, either by the government on suspicion of being a terrorist, or by fundamentalist groups pressuring him to join their cause.