The chief of criminal investigations for the attorney general in Mexico has announced his resignation while an internal affairs inquiry continues to investigate the handling of a case by his office concerning the 43 university students who went missing almost two years ago.

A government statement said that the resignation of Tomás Zerón de Lucio from his position as head of criminal investigations has been accepted by attorney general Arely Gómez González.

While the statement wished Zerón luck in his future endeavors, it did not delve into the reasons for his departure.  An official for the attorney general’s office suggested that it may have been done in an effort to repair relations with the families of the missing students, who have continued to pressure the government to solve the case while also seeking the removal of Zerón .

It was also noted that Zerón will not be leaving the government in its entirety, as mere hours after his resignation was announced, President Enrique Peña Nieto named him as the “technical secretary” of Mexico’s National Security Council.

While Zerón has been involved in a number of high-profile criminal cases in the country, the largest such case involved 43 male college students.  As undergraduates from a teachers college in Ayotzinapa in the Pacific coast state of Guerrero, the students disappeared in September 2014 during a violent night in the city of Iguala that involved Mexican security forces.

To date, the remains of just one student have been found, writes Kirk Semple for The New York Times.

Many have criticized the government, which has stuck to the story that the men were killed by a drug gang who then burned their bodies and dumped the ashes into a nearby river.  While the former attorney general said that determination was “the historic truth,” independent investigators do not believe it to be the case.

Two large reports were written by a number of foreign human rights and legal experts on the situation after studying the case.  In the end, the reports bring into question the ability of authorities to fully investigate the case, while at the same time raising doubts as to the integrity of the Mexican judicial system.

Zerón himself was singled out in the report, which questioned the events of October 28 and 29, 2014, when Zerón was shown in video clips to have brought a detained suspect to the banks of the San Juan river, where it is believed the bodies were placed.  The videos also show plastic bags that look similar to the ones brought out of the river the following day, said to contain the incinerated bones, including the only fragment to have been found that was large enough to provide a DNA connection to one of the missing students.

Because none of these activities were recorded in the case file, the report maintains that investigators could have manipulated or even planted evidence.

“We hope this resignation can make possible a greater deepening and transparency in the investigation,” said Mario Patrón, director of Miguel Agustín Pro Juárez Human Rights Center, an organization in Mexico City.

“The Mexican state is still in debt to the students’ families and relatives,” he added.