MONTERREY, Mexico -- A prison riot that left 49 inmates hacked, beaten or burned to death opened searing questions about gang rule, extortion and human rights violations in Mexico's overcrowded prisons, where people merely awaiting trial are mixed in with some of the world's most hardened killers.

Those questions were not abstract for Victoria Casas Gutierrez, a cleaning lady who had waited for hours Thursday for news of her 21-year-old son, Santiago Garza Casas, who was facing trial for allegedly acting as a lookout for a criminal gang.

Santiago was sent to the Topo Chico prison in September for missing a parole appointment. He was immediately mixed in with a prison population that included murderers.

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With their gang ties and access to drugs and guns, many say the Zetas and Gulf cartels run the prison.

"They charge taxes, and if the relatives don't bring a certain amount ... they beat them," Casas Gutierrez said. The amounts charged depend on their crimes, but can be thousands of pesos. "Sometimes we have to sell our homes."

"There is vice inside and everything that is in there is their fault, the authorities," she said.

An inmate's family member is helped by a Green Cross worker and a Civil Protection worker outside the Topo Chico prison in Monterrey, Mexico, Feb. 11, 2016. Reuters/Daniel Becerril

Casas Gutierrez was lucky; her son was not on the list of about 40 dead released Thursday, but some bodies were so badly burned it may take days to identify them.

It was a Dantesque scene at the gates of the prison, as terrified relatives waited for more names to go up on the list of the dead posted in two letter-sized sheets on a wall.

"Ayyy, my son is on the list!" 63-year-old Maria Guadalupe Ramirez screamed when she saw the name of her son, Jose Guadalupe Ramirez Quintero, 26. She collapsed into the arms of her daughter and human rights workers.

Ramirez's grief echoed the concerns of others whose loved ones were tossed into Topo Chico, despite being sentenced for minor offenses or even while still awaiting trial.

"He had already gotten out. They picked him up again just for drinking. ... There is injustice in this prison," she said, shaking her fists and sobbing.

Authorities allowed hundreds of relatives to enter the prison Thursday afternoon. But even those who were able to confirm that their loved ones had survived feared for their safety.

One woman, who declined to give her name, visited her brother briefly and said she saw genuine fear on his face. He was only 10 days from his release date after serving nine months for drug possession. "They have threatened them so that they don't talk about what happened," she said. "Only they know, but they don't tell us anything."

"Who is going to assure me that they aren't going do anything else inside," she asked.

No escapes were reported in the clash at the Topo Chico prison in Monterrey, said Nuevo Leon state Gov. Jaime Rodriguez. The riot took place on the eve of Pope Francis' arrival in Mexico, a visit that is scheduled to include a trip next week to another prison in the border city of Ciudad Juarez.

Rodriguez said in the morning that 52 people had died, but he lowered that by three in the late afternoon. The reason for the changed death toll was not clear.

At a news conference the governor read a list of 40 names of confirmed victims, saying five of the remaining bodies had been charred by fire and four were yet to be positively identified. One of the injured was in grave condition.

The fighting began around midnight with prisoners setting fire to a storage area, sending flames and smoke billowing into the sky. Rescue workers were seen carrying injured inmates - some with burns - from the facility.

Rodriguez said the clash was between two factions led by a member of the infamous Zetas drug cartel, Juan Pedro Zaldivar Farias, also known as "Z-27," and Jorge Ivan Hernandez Cantu, who has been identified by Mexican media as a Gulf cartel figure.

But National Security Commissioner Renato Sales Heredia said later Thursday in a radio interview that authorities believe the fight was between two factions of the Zetas for control of the prison.

A turf war between the gangs bloodied Nuevo Leon state and neighboring Tamaulipas between 2010 and 2012. The Zetas once nearly controlled the area around Monterrey.

The situation at the prison was so out of control that even Rodriguez acknowledged to local media that the two cartel bosses "were fighting for control" of the prison.

Mario Martinez was still awaiting word on his father-in-law, who was being held at the prison pending trial. On Thursday afternoon he said the danger of violence inside was well-known long before the riot.

"This (place) was a time bomb," Martinez said. "The authorities should not ignore what the people inside are saying."