Indigenous rights activist Alberta Cariño and Jyri Antero Jaakola from Finland were killed in an ambush by armed men in the Triqui area.
Judges ruled not to change the law, which says extrajudicial killings and acts of torture and rape committed by members of the former military regime were political acts.
All presidential candidates urged to send out a clear message that, if elected, they will put an end to many decades of abuses and impunity.
The authorities have been urged to take immediate action to protect media workers after an escalating series of attacks has led to six journalists being killed in less than eight weeks.
Amnesty International has urged the Mexican authorities to investigate an attack on human rights observers in the state of Oaxaca, that reportedly left at least two people killed and several injured and missing.
Amnesty International has welcomed the conviction of Reynaldo Bignone, who was found guilty of torture, murder and several kidnappings that occured during the 1970s.
The law protects those responsible for thousands of killings and disappearances during the country's armed conflict from 1980 to 1992.