A jury on Tuesday spared the life of a terrorist who killed 11 people in the 1998 bombing of a U.S. embassy in Africa. 

The same jury spared the life of another defendant last month.

In its third day of deliberations, the 12 anonymous jurors said they could not agree on the death penalty for Khalfan Khamis Mohamed, opting instead for a sentence of life in prison without parole.

Mohamed, 27, was convicted May 29 of mass murder for the Aug. 7, 1998, embassy bombing in his native Tanzania. A near simultaneous bombing of the embassy in Kenya killed 213 people.

Tuesday's decision concluded a six-month prosecution resulting in convictions against four men involved in the two embassy bombings — part of an alleged plot by Osama bin Laden, the fugitive Saudi millionaire, to kill Americans worldwide. A dozen Americans were among the dead in the two bombings.

Six other defendants charged in the U.S. government's largest terrorist investigation ever remain in custody awaiting trial. Thirteen more are still at large, including bin Laden.

The jurors, agreeing with a defense argument, found that executing Mohamed might make him a martyr for the terrorist cause. And they rejected the prosecution argument that he posed a future danger to society, even in prison.

Prosecutors portrayed Mohamed as a cold-blooded killer whose terrorist skills were honed in a bin Laden-financed training camp. Evidence showed that he helped build and deliver the Tanzania bomb.

The defendant "has ice in his veins," prosecutor Patrick Fitzgerald said during the death penalty proceedings in U.S. District Court in Manhattan.

The defendant offered no visible reaction to the decision, sitting impassively alongside his lawyer.

The same jury had deadlocked on the death penalty for a co-defendant last month, sparing the life of Mohamed Rashed Daoud Al-'Owhali, 24, of Saudi Arabia. He was convicted in the Kenyan blast.

After Al-'Owhali was spared, 10 jurors said they thought execution might make him a martyr — a point seized on by Mohamed's attorney during his death penalty phase.

"Send him to jail and he'll be quickly forgotten," said defense lawyer David Stern. "Kill him, and you guarantee him immortality."

After building the Al-'Owhali death case on the emotional testimony of victims of the Kenya bombing, prosecutors took a different approach for Mohamed. They focused on a savage attack last year against a prison guard as the defendants awaited trial.

Mohamed was accused of helping his cellmate ambush guard Louis Pepe in a botched escape scheme. A sharpened comb was plunged into Pepe's eye.

Prosecutors argued that the attack, which left Pepe with permanent brain damage, proved Mohamed was a chronic threat who would try to kill again behind bars.

"A life sentence for Khalfan Mohamed is a death sentence for the next guard who makes a mistake," prosecutor Michael Garcia said.

The defense contended Mohamed was an unwitting bystander to his cellmate's breakout attempt.

The two remaining defendants in the current case — Wadih El-Hage, 40, a Lebanese-born U.S. citizen from Arlington, Texas, and Mohamed Sadeek Odeh, 36, of Jordan — were convicted of conspiracy and face automatic life sentences.

All four were convicted by the same jury May 29.

The Associated Press contributed to this report.