An Egyptian military court on Monday acquitted Mohammed al-Zawahiri, the brother of Al-Qaeda's leader Ayman, overturning a death sentence in a new trial, his lawyer and his son told AFP.
The court also acquitted Mohammed Islambouli, whose Islamist brother Khaled assassinated president Anwar Sadat in 1981, they said. They had been convicted of planning militant attacks.
"Thank God, he was found innocent," Zawahiri's son Abdelrahman told AFP by telephone after the verdict.
"We expect him to be released in the next few days," his lawyer Kamel Mandur said.
In 1998, Zawahiri and Islambouli were sentenced on charges of undergoing military training in Albania and planning military operations in Egypt.
Mandur said the trial also acquitted several other former militants including Sayyed Imam Fadl, once the spiritual leader of the Egyptian Islamic Jihad and mentor of Ayman al-Zawahiri.
But Fadl, like the others acquitted, had shunned violence in the late 1990s and engaged in a war of letters with Ayman al-Zawahiri, denouncing Al-Qaeda's attacks.
Islambouli returned from exile in Iran after a popular uprising overthrew president Hosni Mubarak in 2011, joining a number of Egyptian Islamist militants returning to the country after the ouster of their nemesis.
Under the military, which took power after Mubarak's ouster, several jailed Islamist militant leaders have been released, including Islamic Jihad leader Aboud al-Zomor.
The formerly militant Gamaa Islamiya, involved in Sadat's murder, has even formed a party with representation in the Islamist-dominated parliament.
Mohammed al-Zawahiri was released by the military along with other prisoners after Mubarak's fall before the rulers appeared to have a change of heart and had him rearrested within 48 hours.
His son said that Zawahiri had disappeared in the United Arab Emirates and was then secretly renditioned back to Egypt after his sentencing.
He said that in 2001, the United States asked Egypt for help in identifying a charred skull found in caves in Afghanistan's Torah Bora mountains after a battle with Al-Qaeda militants, suspecting it to be the remains of Ayman al-Zawahiri.
The United States asked Egypt for a DNA sample from Mohammed al-Zawahiri, said his son Abdel Rahman.
Following Sadat's assassination, Mubarak took power and led a wide-ranging crackdown on the Islamists.
They in turn conducted bombings and attacks throughout the 1980s and 1990s, culminating in the massacre of more than 60 people, mostly tourists, by Jama'a al-Islamiya militants in a complex of pharaonic temples in Luxor.
Shortly after the massacre, jailed Islamist militant leaders published recantations of violence.
In a May interview, Zomor told AFP that the mass protests that toppled the regimes in both Tunisia and Egypt had sapped support for militant groups because they showed there was another way to confront tyrants.
"They have created a new mechanism to hold regimes accountable," he said. "This has lessened the support and importance of armed struggle."