MEXICO CITY — The local authorities in Veracruz State declared the case closed. Members of a drug gang had confessed to one of the state’s most notorious crimes in recent months: the murders of three photojournalists and a newspaper publicist.

But as soon as the arrests were announced on Wednesday, questions began to surface, beginning with the most obvious one. Why would the seven suspects, picked up on drug and weapons charges, spontaneously admit to far more serious crimes, in this case four brutal killings?

Mexico has become one of the most dangerous places in the world to be a reporter, with Veracruz as ground zero, according to journalist protection groups. Despite government promises that such murders will not go unpunished, there have been only a few arrests in prominent cases over the past several years, often accompanied by shaky evidence.

As violence between warring drug gangs has escalated in Veracruz over the past year, nine reporters and photographers have been killed in the state, putting pressure on the local authorities to solve the crimes.