Mexico City, Mexico (CNN) -- The shooting death of a Mexican journalist last week was not due to his work but was related to a "personal problem," a Chihuahua state attorney's office spokesman said Monday.
"His murder is not related to his work as a journalist," spokesman Carlos Gonzalez-Estrada said.
The announcement came one day after the newspaper for which slain photographer Luis Carlos Santiago Orozco worked published an open letter to the drug cartels operating in Ciudad Juarez, across the border from El Paso, Texas.
The letter, written by the editorial staff of El Diario newspaper, pleaded with the drug gangs to end violence against journalists.
"You are, at present, the de facto authorities in this city," the Juarez newspaper's letter to the cartels said, "because the legal institutions have not been able to keep our colleagues from dying."
Santiago, 21, was killed Thursday evening while sitting in a parked car outside a shopping mall in Juarez. He was the second journalist from the paper to be killed in the past two years.
He was shot multiple times from close range. A colleague in the car was wounded.
"We do not want more deaths," the newspaper's letter to the cartels said Sunday. "We do not want more injuries or even more intimidation. It is impossible to exercise our role in these conditions. Tell us, then, what do you expect of us as a medium?"
The letter continued: "This is not a surrender. Nor does it mean that we've given up the work we have been developing. Instead it is a respite to those who have imposed the force of its law in this city, provided they respect the lives of those who are dedicated to the craft of reporting."
The local El Diario newspaper has made a reputation for aggressively covering the drug violence in Juarez.
Santiago's death came amid growing violence against journalists, particularly those covering a raging drug war that has seen more than 28,000 people killed in less than four years.
Last week, the lawyer for a Mexican TV cameraman abducted in July after reporting on problems at a prison said his client would seek asylum in the United States because he fears criminals will kill him.
Alejandro Hernandez Pacheco, a cameraman for the Televisa Torreon station in the border state of Coahuila, was one of four journalists kidnapped while covering the arrest of a prison warden in neighboring Durango state and a prison riot that followed.
The abductors wanted to use the journalists, who were connected with some of Mexico's largest news organizations, to force the media to transmit messages alleging corruption by some public officials under the influence of rival drug gangs, Mexican federal Police Commissioner Facundo Rosas Rosas said at a televised news conference in early August.
The journalists escaped or were rescued within days. Others have not been so fortunate.
"Twenty-two journalists have been murdered since President Felipe Calderon Hinojosa took office in December 2006, at least eight in direct reprisal for reporting on crime and corruption," the independent and nonprofit Committee to Protect Journalists said in a special report this month. "Three media support workers have been slain and at least seven other journalists have gone missing during this period. In addition, dozens of journalists have been attacked, kidnapped or forced into exile."
CNN's Rafael Romo contributed to this report.