Gladys Rubina is "outraged" that the soldiers who killed her sister in a massacre three decades ago, during Peru's bloody war between the government and left-wing rebels, could walk free.
Last month, the country adopted a statute of limitations for crimes against humanity committed before 2002.
The law will effectively shut down hundreds of investigations into alleged crimes committed during a conflict that ran from 1980 to 2000 and claimed an estimated 69,000 lives.
"I feel outraged, it makes a mockery of us, they're giving a second chance to the murderers of our relatives," Rubina told AFP at a monument in Lima that marks one of the darkest periods in Peruvian history.
The conflict saw the state battling leftist insurgent groups, notably the Maoist Shining Path guerrillas, with atrocities and massacres committed by both sides.
Rubina, 50, lost her 16-year-old sister Nelly in one of the most high-profile cases now headed for judicial oblivion.
On November 3, 1991, six hooded soldiers entered a house where a party was being held in the Barrios Altos neighborhood of the capital, Lima, and opened fire on what they thought were insurgents.
Fifteen people, including Nelly, were killed in what was said to be an intelligence error.
The same military death squad, known as the Colina group, executed nine students and a professor from La Cantuta University in Lima the following year.
Gisela, the sister of 20-year-old student victim Enrique Ortez, said she was stunned by the "injustice" of the new statute of limitations.
"For more than 30 years, family members in the La Cantuta case have insisted on the right to know who is responsible and to punish those guilty of the crime," the 52-year-old said.
- A boon for Fujimori -
The Peruvian justice system determined that the 25 victims of the two massacres were civilians with no ties to the guerrillas.
Some soldiers were convicted and imprisoned, but others fled.
Both cases were instrumental in the conviction of former president Alberto Fujimori, who spent 16 years in prison for massacres committed by army death squads before being freed on humanitarian grounds last December.
The new law is seen as a boon for 86-year-old Fujimori, who has announced a presidential run in 2026 despite ongoing health issues and pending charges in another case involving the Colina squad.
Gloria Cano, a lawyer for the victims, believes the change will not only halt ongoing proceedings, but possibly also allow for crimes against humanity convictions to be overturned.
Lawmaker Fernando Rospigliosi, however, said the law corrected an anomaly by which police and soldiers can be prosecuted for alleged crimes committed "30 or 40 years ago," while Peru's statute of limitations is 20 years.
The measure -- which automatically annuls about 600 cases involving state actors -- has been criticized by the United Nations and the Inter-American Court of Human Rights.
It did not spark protests in Peru, however.
Gisela Ortiz, a former culture minister and relative of a victim, told AFP it was increasingly only families and lawyers who were fighting for justice for the victims of the massacres.
"There is no social support... for what we are experiencing," she said, also highlighting the "damage that impunity does to our democracy."