Authorities in Mexico's violence-plagued Veracruz state bungled an inquiry into the murder of a reporter probing alleged links between drug cartels and politicians, an investigation by fellow journalists alleged Sunday.

Prosecutors maintained that robbery was the motive for the killing of Regina Martinez, a correspondent for the news magazine Proceso found strangled in her home in April 2012 in Veracruz.

Sixty journalists from 25 media outlets worldwide including Proceso said they spent 10 months pursuing Martinez's unfinished investigations as part of "The Cartel Project" coordinated by the Paris-based group Forbidden Stories.

They criticized the official inquiry into her murder as "flawed" and suggested that the man convicted for her death, Jorge Antonio Hernandez, known as "El Silva," was merely a scapegoat.

Much of Martinez's work focused on two Veracruz state governors, Fidel Herrera and Javier Duarte.

Before her death she was preparing to publish an "explosive investigation" into thousands of people who had disappeared in Veracruz, according to the findings of the collaboration, named "The Cartel Project."

"I think that the mass graves could have been the straw that broke the camel's back," an unnamed high-level government official was quoted as saying.

According to Proceso, the Veracruz authorities "deployed a political, media and legal operation to impose at all costs the version" that Martinez was murdered by two thieves.

The investigation, in which AFP was not involved, found that the "official narrative" about the killing was spread online through "an organized disinformation campaign" using fake social media accounts.

Regina Martinez is one of more than 100 journalists murdered since 2000 in Mexico
Regina Martinez is one of more than 100 journalists murdered since 2000 in Mexico AFP / Sergio Hernandez Vega

A federal investigator from the Special Prosecutor's Office for Crimes against the Freedom of Expression who was involved in the case was quoted as describing a bungled inquiry.

According to Forbidden Stories, Laura Borbolla recounted "a colossally-flawed investigation that she believes ended with an innocent man behind bars."

She said that police destroyed fingerprints in Martinez's home by using too much revealing powder.

Items such as beer bottles said to have been found at the scene of the murder were not given to her until months later and had been manipulated, according to the journalists' findings.

The investigation found that Borbolla never believed in the conclusion of the state prosecutor that robbery was the motive.

"Looking back on this case puts me into a state of complete anger," she was quoted as saying.

According to one of Martinez's friends, the murder was a way to cover up the truth.

"By killing her, they burned down the library of Babel," he said.

Duarte, who is currently serving a prison sentence for corruption, denied any involvement in Martinez's death.

Herrera did not respond to requests for comment, the reports said.

More than 100 journalists have been murdered since 2000 in Mexico, which rights group Reporters Without Borders regularly ranks as among the world's most dangerous countries for news media.

Of those, 28 reporters have been murdered in Veracruz and eight others have disappeared, most of them during the 12 years that Herrera and Duarte were in power, Proceso said.