The trial comes against a backdrop of 2 days of bloody clashes between police and protesters

The trial comes against a backdrop of 2 days of bloody clashes between police and protesters Pro-democracy activists have pitched their tents once again in Cairo\'s Tahrir Square on Thursday to push for political reforms and to demand that officials found guilty of abuse be brought to justice .
A few dozen activists spent a calm night in the square-- the epicentre of protests that toppled president Hosni Mubarak in February-- after violent clashes in central Cairo that left over 1,000 injured.
\"We will stay in the square until guilty police officers are tried,\" Mossaad Shahrur told AFP.
\"We want real, open trials of corrupt police and officials, including Mubarak,\" said Mohammed Abdel Awi.
Activists are also calling for the trial of former interior minister Habib al-Adly, who is being investigated for ordering the killing of protesters during the January 25 uprising.
Adly has been sentenced to 12 years on corruption charges.
Clashes had erupted on Tuesday evening between protesters and anti-riot police, amid conflicting reports of what exactly sparked the trouble.
The interior ministry blamed families of the victims killed in the uprising, saying that some of them stormed a theatre where a memorial service was being held for those who died, which led to clashes with security.
Some activists said police beat the families who had been barred from joining the service, and accused loyalists of the ousted leader of stirring up trouble and instigating clashes.
After the theatre incident, protesters headed to Tahrir Square and were fired at with heavy tear gas. Some broke pavement blocks to throw stones at the police.
Violent clashes also erupted outside the interior ministry building just blocks from Tahrir Square, where the army had to step in to restore calm.
The clashes signalled the mounting frustration with the military rulers over the pace of reform.
On Wednesday, the April 6 movement -- a key pro-democracy group-- called for an open-ended sit-in in Tahrir until the goals of the revolution are met.
Among the key demands are the trial of officials and police officers in abuse cases before and after the January 25 revolt, an end to military trials of civilians, an inclusive political process and freedom of expression and media.