A detailed forensic analysis of video recorded in Cairo on Jan. 24 strongly suggests that an Egyptian police officer fired the shotgun pellets that killed her, Human Rights Watch said in a report released on Sunday.

The rights group’s investigation of the fatal shooting of Shaimaa al-Sabbagh, 31, compared the testimony of four witnesses with evidence from video and photographs recorded before, during and after the Egyptian police used force to disperse a small group of socialist activists who were marching to Tahrir Square with flowers. The march, on Jan. 24, was in memory of more than 800 protesters killed in the 2011 uprising that began with antipolice street protests that Jan. 25, national Police Day in Egypt.

According to the Human Rights Watch analysis, an examination of video posted online by the Egyptian newspaper Youm El Sabea shows Ms. Sabbagh crumpling to the pavement a split second after a masked officer fired a rifle in her direction from close range.