From his rickety apartment in the shanty-lined hills of Colonia Libertad, Giovanni Rubio said he witnessed a Border Patrol agent fatally shoot a man who had crossed onto U.S. soil.
"We want him electrocuted, and we want to watch," said Rubio, 22, referring to the agent whose actions sparked an international furor.
Homeland Security Secretary Michael Chertoff, visiting San Diego last week, offered his own take on the increasingly volatile situation on the border: "Anybody who assaults an agent is asking for trouble."
The differing reactions to the shooting on one of the most violence-prone stretches along the 2,000-mile border with Mexico illustrate the deepening cultural gulf between two nations separated by an increasingly fortified frontier.
While Mexican politicians have condemned the shooting and demanded a federal investigation, the U.S. response has been restrained, punctuated by outbursts of tough talk.
"When something tragic like this happens, it's something that Mexico interprets as a human rights violation, and conversely in the U.S., we tend to see this as an issue of the law," said David Shirk, director of the Trans-Border Institute at the University of San Diego. "So there's tension between competing notions of fairness and justice."
In Mexico, the Dec. 30 shooting of Guillermo Martinez Rodriguez, 18, topped media coverage all last week -- "Shot in the back," blared one headline -- and prompted President Vicente Fox's administration to make a formal request for an investigation.
The shooting has prompted analysts on both sides of the border to repeat long-standing criticisms of each country. Mexico, critics say, has failed to provide economic opportunities for its people and hasn't done enough to help the plight of migrants. U.S. policies, say others, have failed to fully address the issues driving illegal immigration.
And though the U.S.-Mexican War of 1846-48 may be a foggy historical fact for many Americans, in Mexico it's an old humiliation that still stings, and border activists have invoked it when demanding justice for Martinez.
"Guillermo Martinez Rodriguez, you will be remembered, my brother, and your name and story will be heard from coast to coast. We demand an end to the genocide of the Latino community by the ... continued militarization of the border," said Enrique Morones, president of the Border Angels, a San Diego-based immigrant rights group.
Amid the rhetoric, an unusual level of cooperation has developed between law enforcement officials in both countries.
On Thursday, Mexican federal authorities handed over two witnesses to state and U.S. federal authorities at the San Ysidro border crossing. The witnesses, one believed to be the dead man's brother, were immediately taken to where the incident occurred.
From the Colonia Libertad neighborhood of Tijuana, residents marveled at the incongruous site of so many black-suited, heavily armed men dirtying their leather shoes on the muddy, garbage-strewn hillsides.
"Everybody is really interested," said one 6-year-old boy outside his tar paper shack.
Since the shooting, Mexican law enforcement agencies have stepped up patrols to discourage crossings and have agreed to erect signs warning people that assaulting U.S. agents is against the law.
On the evening of the incident, the agent, an eight-year veteran, encountered a man who had jumped the first border fence and was holding a ladder near the second, 15-foot wall, according to Border Patrol accounts provided to the San Diego Police Department, which is leading the investigation.
The man appeared to throw a rock, prompting the agent, whose name has not been released, to fire a single shot, police say. Because the wounded man fled back to Mexico, U.S. authorities say they haven't been able to confirm his identity.
Mexican officials said Martinez was taken to a Tijuana hospital and died the next day. He was shot in the back from about 16 feet away, according to the Mexicans' preliminary investigation.
Mexican media have portrayed Martinez as a hard-working father of two who had crossed into the U.S. in search of work.
But Border Patrol officials said Martinez was a smuggler who had been arrested 11 times on suspicion of guiding migrants across the border.
Martinez lived in a tiny apartment in Colonia Libertad, a notorious hub of smuggling activity. The border separating "La Libertad," as locals call it, from San Diego is a heavily contested stretch that is a microcosm of the larger border enforcement problem.
For residents here, the rusty fence is an ugly, offensive and unnecessary barrier to California, where many people work or have family.
Martinez, many residents say, was a smuggler, but he didn't deserve to be killed for helping people reunite families or realize their dreams.
"It was a rock against a bullet," said Ignacio Montano, 36, a Colonia Libertad resident, who called the agent's actions excessive.
But to Border Patrol agents, Colonia Libertad is a hostile place of hardened criminals, and Martinez's behavior typified the increasingly dangerous tactics used by the area's gang members.
When agents erect cameras, smugglers shoot them down. When agents use pepper ball launchers, gang members fire back with ball-bearing-loaded slingshots. Gang members wear bandannas and dress in layers of clothing, providing extra padding that agents say make the pepper balls ineffective.
When Martinez picked up the rock, agents say, he became a deadly threat. And with assaults against agents reaching record levels, the agent's response was not a surprise.
"We've been warning people," said one longtime border agent who spoke on condition of anonymity. "Now it happens, and everybody's shocked."
Times researcher Cecilia Sanchez in Mexico City contributed to this report.