CAIRO – Ousted President Hosni Mubarak and his two sons were detained Wednesday for investigation of corruption, abuse of power and the killing of protesters, bringing cheers of victory from activists who hoped it marked a turning point in Egypt’s turbulent transition to democracy.

The 82-year-old Mubarak was under detention in a hospital, a step prosecutors depicted as a precaution to monitor his health while under questioning.

His sons Gamal, once seen as Mubarak’s successor, and Alaa, a wealthy businessman, were jailed in Cairo’s Torah prison, where a string of former top regime figures — including Mubarak’s prime minister, ruling party chief and chief of staff — are already languishing, facing similar corruption investigations.

The detention of the man who ruled Egypt unquestioned for 29 years set a new landmark in the already unprecedented wave of upheaval shaking the Middle East. It was arguably the first time an authoritarian leader in the Arab world has been brought to justice by his own people, given that Saddam Hussein was toppled and later captured by American troops, who handed him over for trial and execution by Iraq’s new Shiite rulers.

Corruption had been rife under Mubarak’s regime. In a country where 40 percent of the population lives on $2 a day or less, many resented the business tycoon-politicians elevated to power by Gamal Mubarak and accused of looting the nation’s coffers to enrich themselves.

As Mubarak’s sons were driven away after being taken into custody in the Red Sea resort of Sharm el-Sheikh, where the family has been living since Mubarak’s fall, protesters pelted the police van with water bottles, stones and their flip-flops in a sign of contempt.

The detention was a significant victory for Egypt’s protest movement, which has been in an increasingly tense tug of war with the country’s new military rulers over the shape of the post-Mubarak future.

Protesters have been pushing hard for the apparently reluctant military to prosecute Mubarak. Tens of thousands held the biggest rally in weeks Friday in Cairo’s central Tahrir Square to demand his arrest, and some protesters accused the military of protecting him.

Activists were now watching whether the military leadership is willing to definitively bury the remnants of Mubarak’s authoritarian rule and open up a transition many accuse it of monopolizing.

“The generals don’t know how to absorb that there are two forces,” columnist and activist Wael Abdel-Fattah said, referring to the military and the “revolution” protesters. “They try to say you can rest now, we will do everything. They don’t want to admit that there is another force that also dictates its will.”

“The next steps are for sure more difficult, to build a democratic system: elections, free media, and cleansing the current institutions,” said Abdel-Fattah, a founder of a group pressing for transitional justice in Egypt.

Shady el-Ghazali, a member of the coalition of youth activists who organized the 18-day protest movement against Mubarak, called the detentions “a positive step forward, even if it was late in coming.”

“This is the beginning of the return of trust in the military, but it can only happen if more steps are taken,” he told The Associated Press. “We hope that the message has reached them and that they allow the people to participate in the decision-making.”

Relations have soured in recent weeks between protesters and the Armed Forces’ Supreme Council, the body of top generals that holds power. Activists complain the military has been acting in ways reminiscent of Mubarak’s regime, putting protesters in military prisons, where some were reportedly tortured, or on swift trial before military courts.

Many Egyptians said the generals were heavy-handedly dictating the course of Egypt’s transition and not doing enough to ensure the remnants of Mubarak’s regime don’t retain power and thwart hopes for real democracy. The tensions came to a peak on Saturday, when troops stormed Tahrir Square before dawn, killing at least one protester and arresting dozens of others.

Military generals defended their tactics, saying military courts and “deterrent” action were needed to protect the uprising and prevent the country from descending into chaos. But in a signal they feel the pressure, Maj. Gen. Mohammed al-Assar said this week, “People must be reassured that their demands will be met.”

The very idea of Mubarak being in custody facing possible prosecution would have been unimaginable only four months earlier, when the longtime president’s regime seemed firmly entrenched.

Even after being forced from power, he seemed untouchable, living with his family at a palace in Sharm el-Sheikh, though they were barred from travel and their assets were frozen.

On Sunday, Mubarak issued a defiant prerecorded message — his first address since his ouster — denying the corruption allegations against him and his family and inviting investigators to check his assets.

Prosecutors immediately announced that they would question him. On Tuesday night, Mubarak was taken to a Sharm el-Sheikh hospital because of heart troubles, and prosecutors said they would question him there so his health could be monitored.

The public prosecutor announced early Wednesday that Mubarak was ordered detained in the hospital for 15 days for investigation. Authorities said later they were discussing whether to move him to a military hospital in Cairo. Mubarak has a history of health problems and underwent gallbladder surgery in Germany last year.

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