Mexican President Enrique Pena Nieto says he will pardon an indigenous teacher serving a 60-year jail term.
Alberto Patishtan, 41, was convicted in 2002 for the murder of seven policemen in southern Chiapas state during the Zapatista rebel uprising.
President Pena Nieto said he would pardon him under a new law which widens the scope of executive reprieves.
Human rights groups have argued that Patishtan's trial was flawed and beset by irregularities.
President Pena Nieto said on his Twitter account that the pardon would come into effect on Thursday, when the new law comes into force.
The law, which allows for leniency in cases in which the convict's human rights are considered to have been violated, was passed on Tuesday.
Patishtan, from the indigenous Tzotzil community, was arrested in 2000 following an ambush in Chiapas in which seven police officers were killed.
He has always denied the crime and his lawyers allege that testimony that he was not at the scene of the ambush was not taken into account during his trial.
His supporters say he was set up as a scapegoat at a time when Chiapas was the scene of a conflict between the Mexican security forces and the Zapatista National Liberation Army, a left-wing rebel group fighting for indigenous and land rights.
Patishtan is currently in hospital in the capital, Mexico City, where he is receiving treatment for a brain tumour.
Speaking to Spanish daily El Pais in March, he said he would not give up hope of being freed from jail.
"I am innocent; this is not the place for me, it's not my home, but I never think of the time I have left [to serve] but that sooner or later I will regain my liberty.”