AP/Rebecca Blackwell

Mexican federal police were responsible for the deaths of at least 16 people in Apatzingan, in the heart of the narco-infested state of Michoacan, according to allegations in a new investigative report by Mexican journalist Laura Castellanos.

The report, published Sunday under the title Fueron los Federales (It was the Federales), argues that Mexican federal police in Michoacan were responsible for the the Jan. 6 massacre of nine members of a self-defense group whom the government claims were killed in a friendly fire shootout. The investigative report, published simultaneously in Proceso magazine, journalist Carmen Aristegui’s website and on Univision, alleges the self-defense group was armed only with sticks.

Castellanos' investigative report, which includes video evidence and is based on more than 30 interviews with self-professed survivors and bystanders, has prompted the federal police and the attorney general’s office to open a new investigation of the incident. Initially, the government investigation determined that "practically all the dead people could have been killed by their friends in the cross-fire" and that "it's impossible to know which bullets killed them,” according to Alfredo Castillo, the former federal envoy and drug czar to the state of Michoacan.

The journalistic investigation, which makes wide use of anonymous sources, claims the vigilante group and other protesters were attacked by federal police for occupying the central square. After the vigilantes tried to fight back, police opened fire again, killing and injuring others, according to the report.

Police have yet to comment on the allegations made in the report.

Carmen Aristegui’s website went offline shortly after the report was published on Sunday — allegedly due to numerous cyber attacks, the journalist says. Aristegui, one of Mexico's most renowned journalists, is also fighting a public opinion battle against the Mexican government and her former employer MVS Noticias who she accuses of giving into government pressures and allegedly firing her for publishing a separate investigative report on a housing scandal involving Mexico’s first lady.