Law enforcement officials in Sinaloa confirmed the slaying, and the state prosecutor told reporters that police found 12 spent shell casings at the scene. He was also a correspondent La Jornada, a national newspaper based in Mexico City. His courage was well-known-in 2011, the Committee to Protect Journalists gave him its International Press Freedom Award-and his impact was widespread.
He is at least the sixth journalist murdered in Mexico since early March, an unusually high number even for one of the world's deadliest countries for media professionals.
The cartel is believed to be responsible for an estimated 25% of all illegal drugs that enter the United States via Mexico.
"I reiterate our commitment to freedom of expression and the press, fundamental for our democracy", he tweeted. "This lack of accountability perpetuates a climate of impunity that leaves journalists open to attack". "It's also home to the Sinaloa cartel, which until recently was headed by Joaquin "Chapo" Guzman" - the infamous drug lord who, after a high-profile escape and recapture, has been extradited to the USA and is awaiting trial.
Guzman is now in jail awaiting trial in the United States. Journalists who worked with him said he kept his sense of humor despite the pressures of his job. "Everybody always deferred to his knowledge", Hootson said.
He described Valdez as a warm, friendly man, well-liked by other journalists who frequently sought his help to navigate and understand the complex, unsafe state.More news: Buffett's Berkshire boosts American, Southwest airline bets; sheds Fox
"Today in Sinaloa they killed the most courageous and most admired journalist", Marcela Turati, a Mexican journalist, wrote in a Twitter message.
Mexico is one of the most risky places to be a journalist, with the vast majority of attacks on the press unpunished.
Filiberto Alvarez was killed in Tlaquiltenango on May 2, Cecilio Pineda Brito was killed in Guerrero on March 2, Ricardo Monlui was killed in Veracruz on March 19, Miroslava Breach was shot dead in Chihuahua on March 23 and Max Rodriguez Palacios was murdered in Baja California Sur on April 14.
In response to that, Valdez founded Riodoce with two colleagues.
Valdez wrote several books about Mexico's drug wars, including a volume a year ago on narco-periodismo, or narco-journalism.
Valdez was the author of the books "Los Morros del Narco" and "Narcoperiodismo", the latter of which examined the dangers of covering the links between drug cartels and public corruption in Mexico.