Award-winning journalist Javier Valdez spent years investigating Mexico's violent drug cartels.
A Mexican reporter known for covering organised crime was killed in the lawless state of Sinaloa on Monday.
Javier Valdez was killed when assailants opened fire on his car in the state capital, Culiacan, according to RioDoce, the media outlet he co-founded and where he worked.
He was the fifth reporter killed since March, making Mexico one of the deadliest countries for journalism at a time when murder rates are at their highest since the peak of the drug war in 2011.
Valdez was one of Mexico's most well-known and loved chroniclers of the drug war, winning the International Press Freedom Award from the watchdog group the Committee to Protect Journalists (CPJ) in 2011 for his prolific coverage of trafficking and organised crime.
Mexico is one of the most dangerous places to be a journalist, with the vast majority of attacks on the media going unpunished.
A group of reporters said last weekend a large group, including children, carrying semi-automatic weapons took their equipment while they covered unrest in the state of Guerrero.
Valdez also contributed dispatches to the national daily La Jornada and published a book last year about the dangers facing journalists who report honestly on the rampant crime and corruption gripping Mexico.
Reaction to Valdez's death
Mexican and foreign journalists paid homage to Valdez on social media, describing him as a courageous writer and generous friend whose killers must be brought to justice to deter future slayings.
"Tears in my eyes, hearing of the murder of Javier Valdez Cardenas in Culiacan, one of the best writers and journalists of Mexico," British author Ioan Grillo said on Twitter.
Tears in my eyes, hearing of the murder of Javier Valdez Cardenas in Culiacan, one of the best writers and journalists of Mexico. TRAGEDY.— Ioan Grillo (@ioangrillo) May 15, 2017
Mexican President Enrique Pena Nieto and the US ambassador to Mexico condemned Valdez's killing.
A special federal prosecutor's office responsible for dealing with crimes against freedom of expression said it had started the procedure for opening an inquiry and was sending a team to collect evidence.
"The state must respond to these circumstances," said Sinaloa prosecutor Juan Jose Rios at a rowdy news conference. Journalists shouted questions, asking what would prevent them from being next.