Sondos Reda Abu Bakr, a 17-year-old high school student, was killed Friday by police officers firing birdshot at a demonstration in Alexandria in support of ousted President Mohamed Morsi of the Muslim Brotherhood. And Shaimaa al-Sabbagh, 31, a left-leaning poet and activist, was killed in Cairo. She was a member of a socialist political party that had supported President Abdel Fattah el-Sisi and the military takeover he led in 2013.

Neither of the women was likely to have posed any threat.

Ms. Sabbagh was walking in a small group of fellow party members on Saturday with a wreath of flowers to lay in Tahrir Square to honor demonstrators killed there during previous protests, according to a witness account and a video recording of the scene. When her group took up the Arab Spring chant for “bread, freedom and social justice,” a contingent of masked riot police officers as numerous as the marchers “fired bullets and gas within minutes,” according to a testimonial posted on Facebook by Azza Soliman, a prominent human rights lawyer who was nearby at the time.

In the video, the police officers are seen firing guns from across a narrow street. A friend, crouching down, grabs Ms. Sabbagh around the waist as she stands upright with blood running down her face. Then he is seen hurriedly carrying her away while the gunfire continues. A forensic report said birdshot fired at close range had pierced her lung and heart, according to news reports.

The deaths on the anniversary of the revolt were predictable, rights activists say, because the swift use of firearms has become de facto police policy toward any unauthorized public assembly, especially in downtown Cairo. On the anniversary last year, more than 50 people died in clashes with the police.

But the arresting stories of the two unarmed women, and most of all the vivid images of Ms. Sabbagh’s death, have dramatized the police violence more effectively than any statistics, rights advocates say.