MEXICO CITY — When the government told Cristina Bustamante that her son had been murdered and incinerated in an enormous pyre, that should have been it, the final chapter in the search for her child and the 42 other college students who vanished last September.

And yet, she said, all she and the other parents could feel was a mixture of resignation, betrayal and doubt, as if justice was being swept under the rug by a government more interested in closing the file than in finding the truth.

“We thought, ‘The entire country is going to believe what he just said and we will be left alone, no one will go out to the streets and protest anymore,’ ” she said, referring to an announcement by the former attorney general closing the investigation in January. “And that’s what happened.”

Now, the release of an international report this week contradicting the government’s account of what happened to the missing 43 students has breathed new life into the parents’ hopes, new cynicism into the public’s perceptions of its leaders — and possibly a new awareness inside the government that its tactics need to change.