Protest leaders, however, were more cautious, and repeatedly rerouted the march at the last moment to avoid confrontations, turning down narrow lanes where residents in upper stories sprayed them with water — it was not always clear whether the gesture was in support or in contempt.

In the last mile, the leader of the march, Mohammad Salwan, ordered everyone to get on the metro train for the final approach to the court, and then the protesters dissipated instead of trying to breach barricades set up by pro-military factions.

“We know there are snipers along the route, and we want to avoid losing any more lives,” he said.

Similarly, a protest in Giza was called off after it was threatened by military supporters, and the only other one to be held was in a strongly pro-Brotherhood area, Helwan, in south Cairo. Another march, to the presidential palace in Heliopolis, was also canceled.

“The leadership decided things were getting out of control and they couldn’t afford more casualties,” said a Brotherhood member who writes for one of the group’s publications and who spoke on the condition of anonymity because he was not authorized to speak for the organization.

Even on Saturday, which had seemed relatively quiet, 79 people were killed in violence around Egypt, according to the government press agency, MENA, in an announcement on Sunday. It provided few details.

Brotherhood leaders in particular have paid a heavy price, with the children of many top officials among the dead. They include Asmaa el-Beltagy, the daughter of a senior Brotherhood leader, Mohamed el-Beltagy, killed at Rabaa Square on Wednesday; Ammar Badie, 38, son of Brotherhood spiritual leader Mohamed Badie, shot during clashes on Friday in Ramses Square; Habiba Abd el-Aziz, 26, the daughter of Ahmed Abd el-Aziz, the media consultant to ousted President Morsi, killed at Rabaa from a bullet wound to the head on Wednesday; and the grandson of the movement’s founder.

There were scant details on the prison killings on Sunday, and no explanation for why the victims were inside a prison van and had reportedly taken a prison official hostage.