The Inter-American Commission on Human Rights (IACHR) began its inquiry at the request of the victims' parents in March 2015. Its mandate was renewed once, but the government refused a second extension, saying they had been given ample time.

The year-long investigation revolved around the fate of 43 students from a teacher-training college who disappeared in the city of Iguala in September 2014. Mexican authorities allege the students were detained by local police, who handed them over to a drug cartel. Members of the gang then allegedly killed the students and incinerated their bodies at a rubbish dump in the nearby town of Cocula.

However, that version of events has been rejected by both the IACHR group of experts and another investigative body that analyzed the dump site. To date, the remains of only one of the students have been positively identified by burned bone fragments.

Suspects 'tortured'

According to the report, published by the IACHR on Sunday, a study of 17 of the approximately 110 suspects arrested in the case showed signs of beatings, including, in some cases, dozens of bruises, cuts and scrapes.

The five-member panel - which includes two lawyers from Colombia, a third from Chile, a former attorney general of Guatemala and a Spanish psychologist - also cited medical reports showing "significant indications of mistreatment and torture of the suspects," with some claiming they received electric shocks on their tongues and genitals.

One suspect said he was nearly asphyxiated with a plastic bag, while medical studies also showed that another had been slapped on the ears so hard his eardrums broke and his ears bled.

Government under fire

The 605-page document also criticized the Mexican government for allegedly stonewalling the panel's investigation and reluctantly providing evidence.

"The delays in obtaining evidence that could be used to figure out possible lines of investigation translates into a decision [to allow] impunity," the report said, adding that the group had also "suffered a [media] campaign that seeks to discredit people as a way to question their work."

"These actions show that some sectors are not interested in the truth," Colombian lawyer Alejandro Valencia told a news conference.

Following the publication of the report, Mexican President Enrique Pena Nieto wrote on Twitter that his government "thanks" the experts for their recommendations and said the attorney general's office would analyze the report to "enrich its investigation."

Amid Mexico's surge in violence and a decade-long drug war, the case of the apparently murdered students has attracted international attention and stirred protests and outrage across the country.