Non-governmental organizations, political leaders and the attorney for Mexican Indian Alberto Patishtan, who was convicted of killing several police officers and sentenced to 60 years in prison, slammed a court's refusal to re-open the murder case.

"It's piling injustice upon injustice. There's acknowledgment from everyone, including members of the appeals court (that received the petition), that Alberto Patishtan is innocent, yet they uphold an inhumane sentence of 60 years" behind bars, leftist leader Cuauhtemoc Cardenas told the MVS radio station on Friday.

The appellate court in Tuxtla Gutierrez, capital of the southern state of Chiapas, ruled Thursday that Patishtan's defense team submitted insufficient evidence to show the Tzotzil Indian, who has been in prison for 13 years, was wrongly convicted.

Patishtan, a teacher who was convicted of killing seven police officers in Chiapas in a trial tainted by irregularities, maintains his innocence.

"I think it's very, very serious that this situation has occurred, that given that Patishtan was not present for the incidents he's accused of this sentence has been upheld, which only shows that we have a totally corrupt justice system, or at least in this case," Cardenas said.

The founder of the center-left PRD party said that "if the executive or the legislative (branches) have the authority to free Patishtan, they should exercise it."

The Indian man could be freed if President Enrique Peña Nieto pardons him, though legally he would still be considered guilty, or if he receives congressional amnesty.

Chiapas Gov. Manuel Velasco said on Twitter he favored the first option: "Unjust that they have refused to free the teacher Patishtan. We demand a pardon."

Patishtan, a supporter of the Chiapas-based Zapatista Army of National Liberation, or EZLN, which launched a short-lived armed uprising in 1994, said Thursday from prison that he was angry about his situation but felt "calm."

"While we're alive, hope doesn't die," he added.

The Indian man, however, refused to ask the president for a pardon, insisting he did not kill anyone.

"That's not up to me. It would be the executive authority in this case that has to do it. For me to ask would be shameful ... because I truly have not killed. I'm innocent," he said.

London-based human rights group Amnesty International also slammed the court's ruling, saying it confirmed that Mexico's justice system was incapable or unwilling to correct injustices. EFE