A man whose beating was broadcast on live television, enraging the Egyptian opposition, has blamed police for the abuse after initially claiming they saved him from protesters.
The presidency described the footage of police dragging and abusing the naked man during deadly clashes outside the presidential palace on Friday as "shocking" and prompted the interior ministry to order a rare investigation.
But in a series of twists since, 50-year-old Hamada Saber first insisted in interviews from his police hospital bed that police had saved him from protesters who beat and stripped him.
An image grab taken from Al-Hayat TV purportedly shows Egyptian riot policemen dragging and beating Hamada Saber.
Mr Saber then changed his account, which was bitterly contested by relatives who said he was being coerced, when prosecutors showed him the video footage, the official MENA news agency reported.
The footage confronted Islamist President Mohamed Morsi, whose movement was banned under ousted leader Hosni Mubarak, with uncomfortable parallels with the old regime.
His office said it deplored the incident but described it as an "isolated act".
It also outraged Mr Morsi's critics, who compared the incident with police abuses under Mubarak.
Two people were killed in clashes on Friday, including a man who succumbed to bullet injuries on Sunday, a hospital official said.
Protesters again clashed sporadically with police outside the palace overnight on Saturday, without reports of casualties.
One of the protesters said they were there to pay homage to a young man killed on Friday, and they chanted "Leave!" and "The people want the regime to fall!" - slogans used two years earlier during the uprising that overthrew Mubarak.
The main opposition National Salvation Front (NSF) has called for the resignation of Interior Minister Mohammed Ibrahim over Mr Saber's beating.
Mr Ibrahim ordered an investigation into the incident and said he would resign if "that's what the people want", his office said.
Prosecutors had earlier said Mr Saber, a 50-year-old construction painter, was found carrying petrol bombs.
Clashes over the past week have widened the gap between the presidency and the opposition.
The Freedom and Justice Party, the political arm of the Muslim Brotherhood movement from which Mr Morsi hails, accused the NSF, led by failed presidential candidates, of trying to take the presidency by force.
"Being a witness to violence and the armed militias of the NSF, people now know the assailants are trying to take over the presidency by force after being defeated in the vote," a commentator wrote in the party's newspaper.
Egypt's highest court, the Supreme Constitutional Court, on Sunday postponed until March 3 a ruling on the legality of the Islamist-dominated commission that drafted a contested new constitution for Egypt, state media reported.
The charter has divided Egypt, pitting Mr Morsi and his backers against the opposition, which includes secularists, leftists and Christians as well as Muslims.