Updated

Egypt launched Monday an investigation of the country's former military rulers for their alleged role in the killing of protesters during their nearly 17 months in power, an unprecedented civilian probe into the affairs of an army that has traditionally shielded itself from outside scrutiny.

International and local rights groups have pressed Egypt's newly elected president to hold to account the council of military officers who ruled the country from the February 2011 overthrow of Hosni Mubarak to this summer. At least 120 protesters died in clashes with security forces and soldiers during this time.

A court official named judge Tharwat Hamad as leading the probe of accusations against Field Marshal Hussein Tantawi, head of the Supreme Council of the Armed Forces, and the other generals who sat on the body that ran Egypt during the 17-month transitional period. The official spoke on condition of anonymity because he was not authorized to speak to reporters.

But investigation is up against what rights groups call the military's culture of impunity, as well a decree passed by SCAF before giving up power that protects members from civilian investigation even after they are out of service.

Some lawyers have questioned whether civilian investigators will be able to take key steps like summoning the generals for questioning.

Hamad might be able to find a legal way around the ban, for example, summoning the generals in their capacity as political leaders at the time. But lawyers like Basma Zahran — who represented the families of some of the 26 Coptic Christian protesters killed in an October 2011 march — are skeptical that he will do so.

She says Hamad was in charge of part of that investigation. She says the judge admitted at the time that he was unable to summon commanding officers as accused or even witnesses, and ended up shelving the case probing the deadly shooting of 11 civilians. A separate military tribunal ended up convicting three soldiers of manslaughter and sentencing them each to two years in prison for the crushing of 15 civilians under armored vehicles.

Zahran dismissed the new probe as a "publicity stunt." Hamad could not be reached for comment.

Egyptians have filed over 100 complaints with the country's prosecutors against the military rulers, including Tantawi, Chief of Staff Lt. Gen. Sami Anan, and other generals who sat on SCAF.

The generals transferred power to the country's first elected and first civilian president, Mohammed Morsi, at the end of June. But the period before that handover was marred by violent clashes with protesters who accused the generals of mismanaging the country, or doubted their intent to step down.

Council members did not address accusations of killing protesters, while military officials frequently accused protesters of attacking troops. It was not immediately possible to contact any of the now-retired generals.

President Morsi moved quickly after taking office in June to cement his authority over the generals, cancelling a SCAF decree that granted the military powers that undercut his own.

He has promised the protesters' families that he would mete out justice against those responsible for the killings. Weeks after he took office, he retired Tantawi and Anan from active military service, replacing them with a new defense minister and chief of staff. But he also granted the two officers the country's highest honors and named them as advisors, raising fears that the generals may evade responsibility for alleged abuse during their rule.

In two extensive reports released this month, the London-based Amnesty International urged Morsi to ensure full and impartial investigation into abuses by the military and police during the transition, saying a culture of impunity only allows them to continue.

Amnesty said the army's response to protests was "disproportionate," citing cases when live ammunition was fired in response to the lobbing of stones or firebombs.

"Both the ordinary and military judiciary failed to provide an effective remedy for the victims, so their suffering continues and the military forces remain confident that they are above the law," Amnesty said. "If Egypt is to turn the page on decades of abuse, the army should not remain beyond the reach of the law."