An appeals court ruling is threatening to derail Mexico's effort to prosecute suspects in one of its most notorious crimes of recent years: the disappearance and presumed murder of 43 students in Guerrero state.

The injunction orders the state judge overseeing the case to correct flaws in its case against 22 police officers who are accused of killing four people on the night the students vanished. It was issued late last year but not yet publicized.

The case of the missing students is one of the most widely protested examples of human rights abuses in Mexico's recent history and it's shaken faith in all levels of government.

The injunction found prosecutorial errors including inconsistent testimony and scant evidence, and said if they cannot be fixed, the accused must be exonerated.