An Egyptian court acquitted six police officers Saturday on charges of killing 83 protesters during the country’s 2011 revolution, the latest in a string of trials that rights group say failed to hold the country’s security forces accountable for demonstrators’ deaths. The acquittals come as ousted Islamist President Mohammed Morsi, toppled in July by the military, faces a host of criminal charges. Morsi appeared Saturday in court and shouted from inside a soundproof defendants’ cell, urging his supporters to continue protests and vowing to try the country’s military chief and Republican Guards commander for killing his supporters. The police officers’...