The horrific case of 43 college students from the Mexican village of Ayotzinapa who disappeared in September 2014—allegedly murdered by a local narco-gang—made deeply embarrassing international headlines again this week. The New York Times reports July 10 that sophisticated spyware supplied to Mexico officially to track narco-traffickers and terrorists was instead used against human rights investigators looking into the Ayotzinapa case.

The spying took place during what the investigators called a "broad campaign of harassment and interference" that prevented them from solving the haunting case, the Times reports. This was also just before the group issued its final, damning report in April 2016.

Further details are provided by Forbes. The revelation was made by a digital forensics team at University of Toronto's Citizen Lab, which found that text-messages sent to the Group of Independent Experts (GIEI) contained the spyware.

Produced by a secretive Israeli firm known as the NSO Group and costing tens of millions of dollars, the "Pegasus" spyware has been used against Mexican politicians, activists and journalists. Generally, the target would be sent a message or e-mail containing a link that would infect their device with the spyware. The main contact person for the GIEI was apparently sent such a message, although it is not clear if the link was clicked on.

"We speculate that the operators behind these attempts may have sought to learn the theories, sources, and substance of the investigation as the final report was being prepared," Citizen Lab wrote.

The Mexican government has now promised an investigation into the spyware scandal, which means that investigations are heaping on investigations. The Ayotzinapa families meanwhile still wait for justice. There have been no convictions in the case, and the remains of only two of the missing students identified.