[3] In 2003, he and other reporters from the daily newspaper Noroeste founded Ríodoce, a weekly dedicated to crime and corruption in Sinaloa, considered one of Mexico's most violent states.

In September 2009, Ríodoce published a series on drug trafficking entitled "Hitman: Confession of an Assassin in Ciudad Juárez."

One morning a few days after the conclusion of the series, a grenade was thrown into Ríodoce's office, damaging the building but causing no injuries.

[9] Later in the same year, the trustees of Columbia University awarded Ríodoce the Maria Moors Cabot Prize for journalism that contributes to "inter-American understanding".

[10] On May 15, 2017, Valdez Cárdenas was shot 12 times and killed by unidentified gunmen around noon, blocks away from the Ríodoce offices in Culiacán, Sinaloa[11][12] when he was 50 years old.