The three women said Wednesday their phone calls had been traced and they had been placed under surveillance.
The case involved journalist, Marcela Turati, lawyer Ana Lorena Delgadillo, and Mercedes Doretti, the co-founder of a forensic investigation team.
“This is not just an attack against us, it's an attack on democracy,” said Delgadillo.
All three have spent years investigating the cases of Mexico's approximately 93,000 “disappeared,” mostly people thought to have been killed by drug cartels, their bodies dumped into shallow graves or burned.
In 2011, authorities found 48 clandestine graves containing the bodies of 193 people in the northern border state of Tamaulipas. Most had their skulls crushed with sledgehammers, and many were Central American migrants.
It was later revealed the victims had been pulled off passing buses by the old Zetas drug cartel, and forced to fight each other with hammers or be killed, if they refused to work for the cartel.
But instead of spending its time looking for the killers, the federal attorney general’s office decided to investigate the researchers in 2015 and 2016 for alleged organized crime violations.
On Wednesday, the three investigators appeared at a news conference with human rights groups and relatives of the victims killed in 2011, to say the investigation against them posed a threat to the rights of victims to be represented and to find out the truth.
“We were seeking justice, we were trying to prevent impunity,” Delgadillo said, adding the three have filed a complaint against the prosecutors' office.
Doretti's forensic experts team has also been involved in the investigation of the disappearance of 43 students in the southern state of Guerrero in 2014, a case that also embarrassed the government. Prosecutors also mishandled that investigation, and charges have been filed against former officials in that case.