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 on 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.

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.

Casas Gutierrez was lucky; her son was not on the list of about 40 dead released on 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 court 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.