Soldiers killed as many as 15 people after they surrendered in an abandoned warehouse in southern Mexico last summer, according to a scathing National Human Rights Commission report that lays out allegations of threats, torture, fake autopsies and crime-scene manipulation designed to cover up the illegal acts.

The commission's report released Tuesday gave the most gruesome version yet of what happened in the June 30 mass killing of 22 alleged gang members, contradicting the army, which said all died in a fierce gun battle after soldiers came under fire in the town of San Pedro Limon. Three of the victims were teenagers.

Calling it "one of the most serious human rights violations that can be committed," Commission President Raul Plascencia issued a report challenging all official versions to date and called on prosecutors to investigate the cover up. The recommendation is not binding, but by law the government must publicly explain its reasons if it does not comply.

So far, eight soldiers face disciplinary charges and three are charged with homicide for an incident the army and the Mexico state prosecutor's office initially denied happened. The federal Attorney General's Office didn't take up the case until three months afterward, according to the human rights report.

No higher-ranking officers have been implicated so far, but the commission also called on the authorities to extend the investigation to those who subsequently visited the scene, including the commander of the 102nd Infantry Battalion of the 22nd Military Zone, to which the soldiers belong.

The army, attorney general and Mexico state prosecutor's offices all declined to comment on the report late Tuesday.

The commission investigation showed that the crime scene was altered to mimic the army's official version of a shootout. "The scene was so altered that some bodies were moved, and weapons were placed on all the dead bodies lying in the dirt," Plascencia said.

Someone had twisted the head of one suspect until his neck broke. Four other bodies had marks of having been beaten with blunt objects before they were killed. Bullet marks and other evidence indicated that seven others among the dead were lined up near the walls of the warehouse and shot "when they were disarmed and were not resisting," Plascencia said.

The report says survivors of the shooting were tortured and threatened with sexual violence to support the army's version of events, and prosecutors in Mexico state altered autopsies.

The army's official story came under suspicion almost immediately because only one soldier was injured in what was described as a long, intense exchange of gunfire. The Associated Press visited the scene three days after the incident and found little evidence of a shootout, but bullet markings indicating some of the dead were shot at close range.

A witness to the killings, who had gone to the warehouse to retrieve her 15-year-old daughter, then told the AP in September that only one person died in the shootout and the rest were shot after they had surrendered. That included her daughter, who was finished off by soldiers as she lay wounded on the ground.

The witness, who did not want to give her name for fear of repercussions, gave the AP accounts of mistreatment and threats of rape at the state prosecutor's office that match the description in the commission's report.

She and two other women were at the warehouse, but were spared by soldiers because they told the troops they were kidnap victims. However, two of them, apparently gang associates, were later charged with weapons possession and are now in a federal jail

The report said prosecutors either tortured the three women to force them to concur with the army's version of events, or allowed unidentified people to torture the women with beatings, partial asphyxiation, sexual aggression and threats of rape if they said what really happened.

"They pulled her hair, punched her in the ribs, and with a shopping bag they covered her nose and mouth, asphyxiating her," the report cites one of the survivors as saying. "It is clear that we are facing a case of aggravated torture."

Attorney General Jesus Murillo Karam gave yet another version of events in late September, saying that most of the suspected gang members died in two shootouts, and eight were later killed by the three soldiers now facing civilian homicide charges.

Murillo Karam said the witness, who was threatened at first to support the army's story, now corroborates his version. When contacted by the AP last weekend about Murillo Karam's statement, she simply said, "I can't talk about this anymore."