The families of 43 students who disappeared a year ago in southern Mexico met with Mexican President Enrique Peña Nieto on Thursday and delivered a letter demanding a new internationally supervised investigation.
A human rights group, Miguel Agustín Pro Juárez, confirmed the letter was given to the president and released a copy.
The letter lays out eight demands, most notably that the students' disappearance be reinvestigated with international supervision. It also calls for an investigation of those responsible for the initial investigation, which the families considered a sham.
"Again and again we ask ourselves how could we trust again in an institution that tricked us," the letter says.
The students disappeared Sept. 26, 2014, in the city of Iguala. They had travelled there to commandeer buses that they wanted to use to attend a commemoration in Mexico City. The federal government has said local police from Iguala and the nearby town of Cocula illegally detained the students and turned them over to the local drug gang Guerreros Unidos, which then allegedly killed them and incinerated their remains. The families have never accepted that version.
The government has said that it has identified two of the students from the burned remains recovered from a river in Cocula.
A team of international experts sent by the Inter-American Commission on Human Rights, which spent six months reviewing the government's investigation, found a number of shortcomings. Specifically, it concluded the bodies of 43 students could not have been burned at the garbage dump in Cocula as the government maintains.
Attorney General Arely Gómez had said that portion of the government's investigation will be reviewed with assistance from top international experts.