CAIRO — Egyptian prosecutors are bringing criminal charges against witnesses who said they saw the police kill an unarmed poet and activist during a demonstration, a lawyer who has seen the charges said on Monday.

The witnesses voluntarily told the Egyptian authorities that on Jan. 24, they had seen a group of riot police officers fire birdshot across a street into the peaceful march, which had been headed to Tahrir Square to lay memorial flowers to mark the anniversary, on the following day, of the Arab Spring uprising here.

The poet and activist, Shaimaa el-Sabbagh, 31, was among the marchers. Photographers captured what the witnesses saw: Ms. Sabbagh died of her wounds in the arms of a friend. Within days, stark images of her death circulated on the Internet and made her a symbol of police abuse, resonating so widely that President Abdel Fattah el-Sisi called for an investigation.

The most prominent witness, Azza Soliman, a human rights lawyer and the head of the Center for Egyptian Women’s Legal Assistance, was having lunch with her family across the street from the march, as she and other witnesses have recounted many times.