The families of 43 students who disappeared a year ago in southern Mexico have given a letter to Mexican President Enrique Pena Nieto demanding a new internationally supervised investigation.

The human rights organization Miguel Agustin Pro Juarez says the letter was given to the president Thursday and has 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.

The students disappeared Sept. 26, 2014, in the city of Iguala. The government has said local police illegally detained the students and then turned them over to the local drug gang Guerreros Unidos, which then allegedly killed them and incinerated their remains.