As a small group of demonstrators torched the front door of Mexico's historic National Palace on Saturday night — with no authorities in sight — Mexico City police were busy grabbing and detaining civilians seemingly at random, sometimes blocks away from the plaza where the blaze took place.
The arrests included a brother and sister leaving a restaurant, a hostess who was yanked from a bar despite protests from her manager, and at least one child, an 11-year-old named Angel Yañez Villegas, human-rights activists in Mexico City said.
Meanwhile, authorities did nothing for at least 40 minutes to stop the violent demonstration taking place at the symbolic seat of Mexico's government. A half-dozen individuals first tried to ram open the large wooden door to the building, then set fire to it several times using a supply of what appeared to be gasoline, witnesses told VICE News.
Others danced and cheered as the door was spray painted. Dozens of press photographers were on hand to document the incident.
The blaze and arbitrary arrests added another layer of tension and conflict between citizens and authorities after weeks of massive demonstrations over the suspected mass murder of 43 teaching students by police and drug cartel members in the state of Guerrero.
During a stop in his seven-day state visit to China and Australia, President Enrique Peña Nieto decried the damage done to the ornate door, which dates to 1852.
"It is unacceptable to use this tragedy to justify violence," Peña Nieto told reporters. "You can't demand justice by acting with violence."
Until Saturday, the Mexico City protests had been peaceful and attended by tens of thousands of people at a time. The torching of government buildings had only occurred in Guerrero. Ayotzinapa Normal School students and other protesters set fire to the city hall in Iguala, where the police attacks took place, and burned the statehouse in Chilpancingo, Guerrero's capital.
On Monday, some activists suggested that the Mexican government sent operatives to infiltrate the protests and attack the National Palace, perhaps to tarnish the image of the peaceful demonstrators.
The building, activists pointed out, is among the most secured structures in the country, protected by Mexico's elite presidential guard. Witnesses said the guards retreated into the building before the fire at the entrance was started.
"How do you get to the front door of the National Palace with a gallon of gasoline without being noticed?" asked Jesus Robles Maloof, a prominent lawyer who was at the Zocalo central square on Saturday night.
"The government finds it must mine this indignation, generate a little bit of fear, to tell people, 'Don't go to the marches, bring it down a bit,'" Robles Maloof told VICE News.
The arrests all occurred away from the scene at the door — one as far as eight blocks away, near Alameda Park, witnesses said. Video shows police in riot gear detaining a 28-year-old man named Luis Villegas Esparza, who was reportedly helping an injured bystander.
All 18 people arrested Saturday were released by Monday morning. Attorney general Jesus Murillo Karam said in a radio interview that they had nothing to do with the violent actions at the palace door. Murillo Karam said one person was freed "with caution" in connection to the fire, but he did not elaborate further.
The random arrests continue a pattern of persistent abuse of bystanders by police during large demonstrations in Mexico City. When Peña Nieto was sworn-in as president on December 1, 2012, dozens of people were detained and one person died after being hit in the head with a projectile fired by police.
Antonio Martinez, a human rights lawyer and activist, called the abuse and random arrests by Mexico City police "systematic."
"It's simply a scandal," Martinez said. "None of those people arrested were at the door."
Mexico City police chief Jesus Rodriguez Almeida defended the actions of his officers on Saturday, saying the bystanders were detained "legally." He said police did not enter the square right away to avoid further confrontations.
"Today we could be lamenting deaths or injuries," Rodriguez said.
A police department spokesperson declined to answer questions from VICE News about the arrests Saturday. A spokesperson for Mexico City's municipal government also declined to answer questions.
A mother of a man who was detained arbitrarily by Mexico City police on Saturday describes his injuries under arrest.
In the latest Guerrero protests Monday, students from the Ayotzinapa Normal School and their supporters occupied and shut down the international airport in Acapulco for three hours. On Saturday, they rammed vehicles into the main gateway of the state government headquarters in Chilpancingo and set them on fire.
The students have vowed to continue the protests. A mother of one of the 43 missing students — who were all declared dead by the attorney general in a press conference last Friday — said the attacks on government buildings were "only a little taste."
"We're going to set fire to the whole country, if they keep up with their little stories," said María Hernandez, whose son Miguel is among the missing 43 students.
Omar García, an Ayotzinapa student leader and survivor of the September 26 attacks, warned the government that if independent forensics investigations determine that his classmates were indeed incinerated in a dump in the town of Cocula, "the shit will hit the fan" for Murillo Karam and other federal officials.
"Mexico is tired of him and of all them," García told VICE News.
Before Murillo Karam's press conference Friday, a parent recorded video of the attorney general saying it was "possible" the students were killed, although he repeated that he could not know for sure because the remains that have been recovered were severely burned. Specialists in Austria are expected to further examine the charred remains.
VICE News reporter Melissa del Pozo in Chilpancingo contributed to this story.