Leading Mexican human rights groups announced Wednesday that a military court acquitted six of seven soldiers charged with breach of discipline in the 2014 killing of 22 suspects, including between 12 and 15 who were executed after they surrendered.

The announcement by Miguel Agustin Pro Juarez Human Rights Center and others is the latest step backward in accountability for alleged military killings and rights abuses in the country. The sentences were handed down in October but were not made public until now, after the rights groups obtained the documents.

Mexico's government is now less transparent about such confrontations than it was in June 2014, when an army patrol engaged in a brief firefight with the suspects. Most of the suspects surrendered and were then executed, according to witness accounts and a governmental investigation.

One soldier was wounded in what the army initially described as a shootout in the township of Tlatlaya.

Later, only one soldier was convicted by the military court on charges of failure to obey orders. He was sentenced to one year, time which he has already served.

The sentences were handed down in October but were not previously made public. They rights groups obtained the information based on an appeal by the mother of a girl killed at the grain warehouse in southern Mexico under a rule that allows victims or relatives access to court proceedings.

The ruling by a closed military court "consolidates impunity in one of the most serious violations of the right to life in recent history," the rights groups said in a statement. "This ruling ... comes on the heels of other government actions that show a troublesome tendency to leave the case in darkness."

"The Tlatlaya case is headed toward going unpunished," said a statement by the Pro Juarez Center and the 15 other human rights groups.

While simultaneous charges were filed in October 2015 against the seven soldiers in civilian courts, a civilian judge ruled there was insufficient evidence to try four of the soldiers. It was unclear whether those four were still at the military prison where they have been held since October 2014. Civilian prosecutors have pledged to appeal the judge's decision to dismiss charges against the four, and three soldiers still face homicide charges in civilian courts.

The Mexican army did not immediately respond to a request for information about the sentences.

But journalists and rights investigators now receive less information on army confrontations than they did in 2014, when The Associated Press first visited the scene of the killings and wrote that the physical evidence did not match the army's description of the events.

At the time of the killings in 2014, the Mexican army regularly released press bulletins on confrontations in which suspects were killed by army troops; after the grain-warehouse killings, the defense department largely stopped releasing such information.

And in February, Mexico's transparency watchdog denied an AP appeal to release autopsy reports on 42 suspects killed by federal police in a 2015 gun battle between federal police and criminal suspects. One police officer died on May 22 in what authorities described as a clash with drug cartel suspects at a ranch in the western state of Michoacan, but the lopsided 42-1 death toll drew suspicion.

The National Institute for Information Access last month ruled against a freedom-of-information request filed by The Associated Press in October. The quasi-independent agency ruled the information should be kept as a state secret for five years. The institute took the government's side in denying there was any evidence that human rights violations occurred at the ranch where the shooting occurred.