Three women volunteers who investigated a 2011 massacre of 193 people appeared at a news conference Wednesday after finding out that they had been investigated by the prosecutors as well, possibly because their findings embarrassed Mexican authorities. 

The three investigators have spent years looking into the cases of Mexico's nearly 93,000 "disappeared," thought to have been killed by drug cartels, their bodies dumped into shallow graves or burned.

In 2011, authorities found 48 clandestine graves with the bodies of 193 people in the northern border state of Tamaulipas. Most of the remains had their skulls crushed with sledgehammers. Many of them were identified to be Central American migrants.

It was later reported that the victims had been pulled off passing buses by the old Zetas drug cartel. If they declined to work for the cartel, they were forced to either fight each other with hammers or be killed.

The federal attorney general's office reportedly investigated the researchers in 2015 and 2016 for allegedly being involved in organized crime violations. The three volunteers include journalist Marcela Turati, lawyer Ana Lorena Delgadillo, and Mercedes Doretti, co-founder of a forensic investigation team.

The three women had a news conference together with human rights groups and relatives of the victims of the 2011 massacre. They also stated that their phone calls had been traced and placed under surveillance as part of the investigation. "This is not just an attack against us, it's an attack on democracy," said Delgadillo, Wednesday.

They claimed that the investigation made by the federal attorney posed a threat to the rights of victims to be represented and to discover the truth. "We were seeking justice, we were trying to prevent impunity," Delgadillo said, all three of them have filed a complaint against the prosecutors' office.

Doretti's forensic team of experts was also involved in investigating the disappearance of 43 students in the southern state of Guerrero in 2014, a case that brought embarrassment to the government. Prosecutors were reported to mishandle the investigation, and charges have been filed against former officials in that case.

TOPSHOT-SPAIN-CRIME-TRIAL-DEMO-WOMEN-RIGHTS [Representational image] TOPSHOT - A protester sporting red gloves, takes part in a protest against gender violence in Pamplona on January 7, 2019, after a court ordered to keep the release on bail for five men sentenced to nine years in prison for sexually abusing a young woman at Pamplona's bull-running festival. - The men, who called themselves "La Manada" (the pack) in a WhatsApp messaging group, had been accused of raping a woman, then 18, at the entrance to an apartment building in Pamplona on July 7, 2016, at the start of the week-long San Fermin festival, which draws tens of thousands of visitors. ANDER GILLENEA/AFP via Getty Images