As my colleague David Kirkpatrick reports from Cairo, “Islamist supporters of President Mohamed Morsi captured, detained and beat dozens of his political opponents last week, holding them for hours with their hands bound on the pavement outside the presidential palace while pressuring them to confess that they had accepted money to use violence in protests against him.”

Those protesters were detained and abused during street fighting last Wednesday, which began after supporters of the Islamist president from the Muslim Brotherhood attacked a sit-in by his opponents outside the palace, leading to deadly clashes. Almost as soon as the fighting ended, opposition activists began collecting visual evidence and testimony of the abuse anti-Morsi protesters suffered that night at the hands of the Brotherhood and their allies.

صورة لاثار تعذيب سيد فتحي توفيق ٣٣ سنة احد المختطفين من ملشيات الاخوان ولسه واصل تحقيقات النيابة //t.co/oMTQc1lt — Mohamed Abdelaziz (@Mohamdaziz) 7 Dec 12

The Cairene blogger who writes as Zeinobia gathered more than a dozen images of badly wounded protesters that were posted online shortly after the detainees were turned over by their Islamist captors to the authorities (who later released them without charge).

Among the injured detainees was Yehia Negm, Egypt’s former ambassador to Venezuela, who spoke to The Times about his ordeal.

السفير يحيى نجم اول ما وصل //t.co/WNP4TBZr — NadimX (@NadimX) 6 Dec 12

Zeinobia also pointed to a widely circulated video clip of Mr. Negm describing his captivity, in which he said that even doctors from the Muslim Brotherhood mistreated the detainees.

Days later, when Mr. Negm appeared on Egyptian television to discuss the torture, his face was still badly scarred.

A sense of the religious and sectarian fervor that drove some of the president’s supporters during Wednesday’s clashes can be glimpsed in a video shot mainly behind Islamist lines by an opposition activist named Abdo Zineldin.

Mr. Zineldin, 20, told The Lede in an e-mail that he is from Shubra, a working-class Cairo neighborhood, and recently learned to edit video at a workshop hosted by Mosireen, a collective of revolutionary filmmakers.

Explaining why he chose to record behind Islamist lines that night, the young activist wrote: “I found myself in the gap where the two sides were advancing and decided it would be an interesting perspective to get also the opinion of the Muslim Brotherhood members, since I am more familiar with the ‘revolutionaries/seculars.'”

In a still frame from his video, Mr. Zineldin said Islamists could be seen hauling off a captive protester under the watch of a member of the police force.

Last weekend, the independent Egyptian newspaper Al-Masry Al-Youm published one reporter’s harrowing account of what he witnessed during three hours “in a Muslim Brotherhood torture chamber at the presidential palace” on Wednesday night.

Members of the Muslim Brotherhood have since argued that any torture that took place on their side of the front lines last Wednesday was not directed by officials. But the reporter for Al-Masry Al-Youm, Mohamed El-Garhi, wrote that uniformed and plainclothes police officers were present as the torture was carried out by more than a dozen members of the Muslim Brotherhood, “supervised by three bearded men who decided who should be there.” He added:

Opposing protesters were brought to the chambers after being detained by Brotherhood members, who beat them and tore their clothes. The chambers were informal and it was unclear how many there were; when someone was detained, a chamber would be established anywhere near a building. The kidnappers would take the detained person’s ID card, mobile phone and money before beginning “investigations,” which included intervals of beating to force the confession that he or she is a “thug.” The interrogators would then ask their captive why they had taken to the street, if they had received any money for protesting, and if they belonged to Mohamed ElBaradei’s Constitution Party, Hamdeen Sabbahi’s Popular Current or the dissolved National Democratic Party of Hosni Mubarak. If the detainee denied affiliation, the torturers would intensify beatings and verbal abuse. They also documented the interrogations on a mobile phone camera.

Watan, an Egyptian news site, published visual evidence of that torture by Muslim Brothers in the form of graphic video recorded during the interrogations of detainees. Taken together, two of the Watan video clips, which show bleeding and battered protesters being pressed to say that they were paid to oppose the president, have been viewed more than a million times in the past week.

After Mr. Morsi claimed in a speech last week that some of those detained had confessed to being armed and paid by the opposition to make trouble, Heba Morayef of Human Rights Watch noted on Twitter that it was remarkable to hear a leader of the Muslim Brotherhood, whose members were routinely tortured into making false confessions by the security forces before the revolution, present such confessions as credible evidence.

Surreal 2 hear an MB president refer to “confessions” obtained by police 2day as evidence when we all know how police usually obtain them — hebamorayef (@hebamorayef) 6 Dec 12

One of the Muslim Brothers who took part in the beating of detainees admitted his role in an interview with Nancy Youssef, a Cairo correspondent for McClatchy Newspapers:

Adel Amer, 44, said he was one of those who beat protesters at a fierce and ultimately deadly standoff Wednesday in front of Egypt’s presidential palace between supporters and opponents of President Mohamed Morsi. Amer said he had to do it. Morsi’s opponents were taking drugs that numb them to pain, he said. The police could not handle the melee on their own, so he and fellow members of the Muslim Brotherhood grabbed them, beat them and handed them over to officers. “We had to beat them so they would confess,” he said, listing their crimes: starting the fighting, bribing others to cause trouble or working to undo the democratic election that Morsi won five months ago. “We had no other option. We protected the police.”

Another attack by Islamists on a high-profile political opponent was reported two nights after the clashes at the palace. On Friday, a former member of Egypt’s Parliament, Mohamed Abu Hamed, was badly beaten by Muslim Brothers as he tried to drive past a rally of Morsi supporters in Cairo.

Mr. Hamed later denied accusations by the Muslim Brotherhood’s political party that he was beaten only after he tried to run over members of the group.

While members of the Muslim Brotherhood were among those killed during last week’s clashes, opposition activists still blamed the Islamists for initiating the conflict by calling on their activists to confront protesters who had gathered outside the palace first.

As Hesham Sallam, one of the editors of Jadaliyya, argued, “regardless of how much violence each ‘side’ has committed,” last week’s fighting was “instigated by a deliberate, conscious decision by Muslim Brotherhood leaders to escalate the conflict with its adversaries.” He continued:

One day after thousands of opposition protesters had marched to the presidential palace and staged a sit-in in order to pressure Morsi into reversing his controversial constitutional declaration, the Muslim Brotherhood called on its supporters to march to the palace. Organizing a march to the same site where Morsi’s opponents are gathered is a tall order, and an inevitable recipe for physical clashes. You do not rally your activists at the same site where your opponents are assembled, expecting a peaceful tailgating picnic.

Activist Ola Shahba who was held and beaten by pro-Morsi for hours recounting her experiences on OnTV. //t.co/fwt6P17Y — Mostafa Hussein (@moftasa) 6 Dec 12

Early Tuesday, one of the protesters who was detained, beaten and sexually harassed by the Islamists, Ola Shahba, reported on Twitter that she was still recovering from her injuries.