It can be deadly to ask questions about multibillion-dollar drug cartels or government corruption in Mexico, where more than 100 journalists have been killed since 2000.

Ninety percent of those cases remain unsolved.

At least five journalists have been killed here so far this year -- casualties in a wave of bloodshed that has left more than 200,000 people dead or missing in the past decade, as Mexico's rival cartels wage war on each other and the army.

The most high-profile case is that of Javier Valdez, a noted crime reporter in the violent western state of Sinaloa who was gunned down on May 15.

As with most of his murdered colleagues, little is known for sure about who killed him and why.

The authorities frequently refuse to provide information, saying they cannot comment on ongoing investigations.

Often, the reality is that "they've hardly done anything," according to Balbina Flores, who runs her own investigations for watchdog group Reporters Without Borders.

One month after Valdez's murder, AFP compiled details on each journalist killed this year and the investigations into their deaths.

- Cecilio Pineda, 39 -

Pineda, the editor of regional newspaper La Voz, was shot by gunmen on March 2 as he relaxed in a hammock near his house in the southern state of Guerrero.

A crime reporter and correspondent for national newspaper El Universal, he had received death threats and escaped an earlier attempt on his life in 2015.

Guerrero state prosecutor Javier Olea said he could not comment on the investigation.

- Ricardo Monlui, 57 -

Monlui, the editor of daily newspaper El Politico, was shot on March 19 as he left a restaurant with his wife and son in the eastern state of Veracruz.

An expert on the state's graft-stained politics, he also wrote a syndicated column.

Veracruz state prosecutor Jorge Winckler declined to comment on the investigation.

Winckler is currently under investigation by a state commission for accusations of systematically obstructing journalists' enquiries.

- Miroslava Breach, 54 -

Breach, a veteran crime and politics reporter for the newspapers La Jornada and Norte de Juarez, was found dead inside her car with gunshot wounds to the head on March 23 in the northern state of Chihuahua.

One of her last stories was on a war between two rival capos in the Juarez drug cartel.

State prosecutor Cesar Augusto Peniche said investigators have "100 percent identified" those responsible: a group of drug traffickers operating in the Chihuahua mountains.

Peniche's office has now closed the investigation, even though no arrests have been made. He said state and federal authorities are working to detain the suspects.

- Maximino Rodriguez, 71 -

Rodriguez, a crime reporter with the blog Colectivo Pericu, was shot as he and his wife parked their car outside a store on April 14 in the northern state of Baja California Sur.

The authorities have arrested four suspects and determined the motive for the killing was Rodriguez's journalism.

According to his colleagues, the suspects are hitmen linked to the powerful Sinaloa drug cartel.

- Javier Valdez, 50 -

Valdez, the founder of weekly newspaper Riodoce, a longtime AFP contributor and author of several books on organized crime, was shot outside his paper's offices on May 15.

He had recently been reporting on a war between rival factions of the Sinaloa cartel since its boss, Joaquin "El Chapo" Guzman, was extradited to the United States in January.

Colleagues suspect the killing was in retaliation for an interview Valdez published with the head of one faction, Damaso Lopez Nunez, who is battling El Chapo's sons for control of the cartel.

State prosecutors have refused to comply with a freedom of information request on their investigation, citing a new law that protects certain information such as suspects' identities.

They initially said they were investigating the case as a robbery. They later acknowledged his journalism may have been the motive

source:AFP