(MEXICO CITY) — Federal police executed at least 22 people on a ranch last year, then moved bodies and planted guns to corroborate the official account that the deaths happened in a gunbattle, Mexico’s human rights commission said Thursday.

One police officer was killed in the confrontation in the western state of Michoacan on May 22, 2015. The government has said the dead were drug cartel suspects who were hiding out on the ranch in Tanhuato, near the border with Jalisco state.

The National Human Rights Commission said there were also two cases of torture and four more deaths caused by excessive force. It said it could not establish satisfactorily the circumstances of 15 others who were shot to death.

“The investigation confirmed facts that show grave human rights violations attributable to public servants of the federal police,” commission President Luis Raul Gonzalez Perez said.

Mexico’s national security commissioner, Renato Sales, who oversees the federal police, denied the accusations, holding his own news conference before the rights commission had finished its own.

Sales said federal police ordered the suspects to drop their weapons and surrender, but were answered with gunfire.

“The use of weapons was necessary and proportional against the real and imminent and unlawful aggression,” Sales said. “That is to say, in our minds they acted in legitimate defense.”

The lopsided death toll had led to suspicions that officers might have arbitrarily killed people during the operation against suspected members of the Jalisco New Generation cartel.

The rights commission questioned the government’s explanation of what led to the clash in the first place.

Federal police had said they encountered a truck and took fire from its passengers before being led to the ranch.

The commission’s report said the government did not produce evidence supporting that account and it said witness statements suggested 41 federal police had sneaked onto the ranch as early as 6 a.m. Officers started their assault at least an hour earlier than they maintained in reporting on the incident, the commission said.

According to the agency’s report, after the federal police officer was shot, police called for backup. Fifty-four more federal police officers arrived along with a helicopter.

The helicopter fired some 4,000 rounds at the ranch house and a nearby warehouse, which caught fire. The helicopter was also hit by gunfire, the report said. One victim died of burns that the commission believes came after he was shot but still alive.

In total, five people were killed by the helicopter, the commission found. One victim was hit by a bullet that entered around his left pectoral muscle and exited his groin, but there were no bloodstains on the jeans he was found wearing, the commission said.

Thirteen of the 22 people the commission said were executed had been shot in the back, it said.

Two witnesses interviewed by the commission said federal police officers told one heavily tattooed man to run outside the ranch house and then the witnesses heard gunshots.

By the time investigators from the state Attorney General’s Office arrived at the scene, “the Federal Police had approximately four hours to manipulate the scene,” the report said.

Eighteen of the victims were found barefoot and one just in his underpants, leading the commission to conclude most were asleep when police arrived. The commission’s investigation said 40 civilians were killed by bullets, one died in the fire and one was run over.

The government had initially refused to release autopsy reports on those killed. The commission criticized the autopsies performed by the Michoacan Attorney General’s Office as being sloppy and incomplete and said the morgue turned over the wrong body to a family.

The case is reminiscent of a 2014 incident in which the commission found that soldiers executed at least a dozen suspected criminals after they surrendered in a warehouse in Tlatlaya west of Mexico City.

The army’s version was that 22 suspects died in a gunfight in which only one soldier was wounded. But The Associated Press found evidence at the scene did not match that account. The warehouse wall showed signs that suspects were lined up and shot.

In that case, three women who survived were tortured by agents of the state prosecutor’s office to corroborate the army’s version.

On Thursday, the commission said two survivors of the bloodshed in Tanhuato had been forced to watch three executions and were then tortured. Police threatened their lives and the lives of their families, it said.