MEXICO CITY (Reuters) - A senior Mexican official who played a central role in the troubled investigation into the 2014 abduction and apparent massacre of 43 trainee teachers has stepped down from a top government crime-fighting agency.


In a statement on Wednesday, the attorney general's office announced the resignation of Tomas Zeron, head of its criminal investigation agency, which came under fire for its handling of the case that has hammered Mexico's reputation. It did not say why Zeron had resigned.


Zeron and officials at the attorney general's office could not immediately be reached for comment.


A panel of independent experts in 2015 sharply criticized the initial government account of what happened to the students on the night of Sept. 26, 2014, in the southwestern city of Iguala, and Zeron was no longer leading the investigation.


But his presence at the top of the agency was a source of friction with the families of the 43 victims, and several senior Mexican officials said privately that Zeron had become an obstacle in the government's efforts to resolve the case.


According to the government's initial findings, the 43 were abducted by corrupt police in Iguala and handed over to a local drug cartel, which mistook them for members of a rival gang.

Then, the government said, they were murdered, incinerated and ground up, and their remains dumped in a nearby river.

It was there on Oct. 29, 2014, that Zeron's team said it found a bone fragment belonging to the only one of the 43 students whose remains have been definitively identified.

But the panel of experts found that Zeron had been to the scene of the discovery a day earlier with one of the alleged gang members, without notifying the man's lawyer or filing a report on his visit.

Zeron denied any wrongdoing, but the attorney general's office by April 2016 had decided to investigate Zeron himself over how he had handled that moment of the search.

Having originally focused its investigation into the missing students on municipal police, the government has widened it to look at the role of federal and state police.

(Reporting by Dave Graham and Anahi Rama; Editing by Peter Cooney)