Villanueva, one of Mexico's most controversial attorneys, was shopping in Monterrey in August when hooded gunmen with automatic weapons tracked her down amid stalls of handbags, perfume and videos, then pumped more than a dozen shots into her body.
The killers delivered a final shot to the head before fleeing the covered market, busy with shoppers at midday on a Sunday.
Villanueva, 56, a single mother known for her combative courtroom manner and for having survived four attacks, was probably the best known among the ranks of Mexican lawyers who practice a particularly dicey specialty: defending accused drug lords.
That club shrank even more later that month, when killers slit the throat of another prominent defense lawyer, Americo Delgado, as he left his home office outside Mexico City. There have been no arrests in either slaying, and Mexican authorities have offered no motives. Officials have not said whether they believe the cases are related.
The unsolved killings have focused attention on the lives of the so-called narcoabogados, or "narco-lawyers" -- important but often-overlooked players in the drug wars that have roiled Mexico for nearly three years. The evolution of narco-lawyers and the violence they increasingly face highlight the weaknesses of a judicial system that is all too often manipulated by powerful drug cartels.
These attorneys range from respected legal whizzes hired to find soft spots in government indictments to briefcase-toting henchmen who take advantage of their jail access to help clients run their drug businesses from behind bars. Some jailed kingpins have employed dozens of lawyers at a time, in part to manage far-flung enterprises: buying and selling properties, paying smugglers, bribing police.
Few drug lawyers seek publicity because of a stigma that often leaves them shunned by colleagues with tamer client lists. Big-name law firms frequently assign rookie staffers to such cases.
It can be dangerous work -- attorneys complain they are increasingly caught up in the country's drug violence. Triggermen might be sent by a rival cartel, dirty cops or even a client disgruntled with the way his case is proceeding.
"They don't want to hear explanations. They hire the lawyer and want a secure outcome, whatever it costs," said Cesar Luis Vea Vea, president of a lawyers federation in the northwestern state of Sinaloa, a drug-trafficking hot spot. "Declining to take on a client can also have risks."
When slayings occur, some say, authorities do little to solve them.
Yet the fees for handling drug cases can be intoxicating, and it doesn't always take superior courtroom skills to win a client's release (a favored method in Mexico is through a judicial ordercalled an amparo). In an opaque justice system rife with corruption, who you know may matter more than what you know about the law.
Drug suspects "seek lawyers who are known to have special influence," said Vea, a former judge.
Villanueva defied many of the usual rules. She went public on behalf of her clients and seemed ever willing to take on more, no matter how radioactive. She represented members of rival cartels. Salty-tongued but devoutly religious, she was a rare woman in a criminal-defense bar dominated by men. Villanueva saved her sharpest comments for corrupt Mexican politicians, and often said they were less trustworthy than drug capos.
When she was killed Aug. 9, Villanueva had a file cabinet full of incendiary cases, including that of a former top federal police official, Javier Herrera Valles. He was jailed last year for allegedly helping traffickers after dismissing the government's drug war as a failure and accusing his boss, public safety chief Genaro Garcia Luna, of corruption.
Villanueva also once represented the man whose testimony helped lead to the 1996 capture of Juan Garcia Abrego, the former chief of the Gulf cartel now imprisoned in the United States. Her recent client list included Noe Ramirez Mandujano, who is charged with taking bribes from Sinaloa traffickers while running the federal attorney general's organized-crime unit.
"She had many open fronts," said Ricardo Ravelo, a Mexico City journalist who interviewed Villanueva for a 2006 book called "Los Narcoabogados."
Villanueva reached folk-hero status after surviving a bombing of her Monterrey office and three shootings from 1998 to 2001. At the time of her death, she bore bullet wounds in her legs, stomach, head and buttocks. Mexican songwriters composed ballads, or corridos, in honor of Villanueva's exploits, calling her the "Lady of Steel" as well as "the Bulletproof Lawyer."
But persistent whispers circulated that her legal work crossed the line into criminal activity. Villanueva was arrested in 2006 in connection with the kidnapping and killing of a federal police official, but was never convicted. She remained unapologetic.
"I'm a lawyer. I don't agree with what my clients do," she told a Mexican newspaper five months before she died.
By contrast, Delgado, who was knifed outside an office he kept in the state of Mexico, plied his trade quietly. Bookish and unflashy in his suit and sensible shoes, the 81-year-old attorney looked more college dean than ace drug lawyer.
Delgado, who like Villanueva was from industrial Monterrey, was considered the go-to expert on extradition cases and was thought to be close to victory in fighting the transfer of Benjamin Arellano Felix, a leader of the Tijuana-based cartel that bears his family's name. Arellano Felix was arrested in Mexico in 2002 and convicted on drug-trafficking and money-laundering charges, but is still sought by U.S. authorities. At one time, he had 41 registered lawyers.
Delgado also successfully fought a U.S. extradition request for Jesus Amezcua, a trafficker from the state of Colima known as one of the "methamphetamine kings."
Associates and others who knew Delgado say he was well aware of the perils of his craft and refrained from promising too much or overcharging.
"He used to say, 'I don't belong to them nor get involved with them,' " said Arturo Arredondo, a Monterrey lawyer who grew up with Delgado and remained close until the Aug. 28 slaying. "He was a technician."
Last year, Delgado was honored for his long legal career by the National Autonomous University of Mexico and a national lawyers federation.
The circumstances of his killing -- a knife assault by three men -- looked more like a robbery than one of Mexico's bullet-riddled gang hits.
But he may have been targeted because of a bloody rivalry between gangs. Delgado most recently served as defense lawyer for Alfredo Beltran Leyva, a suspected kingpin from Sinaloa. Beltran Leyva's faction has been at war with former allies led by Joaquin "El Chapo" Guzman, Mexico's top fugitive.
"To take the case of an important figure, a figure at war with the organization to which he used to belong, is extremely risky," Ravelo said.
During the last year, Delgado may have been in contact with Villanueva, the slain attorney whose former client helped bring down onetime Gulf cartel kingpin Garcia Abrego, Ravelo said. Delgado had been working to win the return of Garcia Abrego on grounds that he was handed to U.S. authorities illegally after his 1996 capture in Mexico.
The killings of the two attorneys have generated fear among people close to the pair. Colleagues at Villanueva's law office, a modest, olive-green house decorated with religious-themed paintings and sculptures, declined to be interviewed. Delgado's family also demurred.
Lawyers in Monterrey have called on authorities in the state of Nuevo Leon to do more to solve the killings, as well as the slayings of other colleagues who handled drug cases. Two were former associates of Villanueva.
"It seems to us very strange that in Nuevo Leon all the crimes against lawyers are unsolved, and we don't know the motives," said Adolfo Trevino, who heads the local lawyers association. "It's due to deficiencies in the investigation."
Lawyers have also been slain in the states of Sinaloa, Guanajuato and Morelos. In March 2008, gunmen stormed a law office in the city of Guadalajara and killed seven attorneys. The firm represented a son of Guzman, the Sinaloa cartel leader, and had defended Gen. Jose de Jesus Gutierrez Rebollo, who was Mexico's drug czar until he was arrested in 1997 on charges of helping the so-called Juarez cartel.
A lawyer who turned up dead in Guanajuato in August appeared in a YouTube video posted later in which he confessed to working for La Familia, a violent drug-trafficking gang. The attorney, Jesus Armando Mancera, said his job was to demand extortion payments from merchants and vendors of pirated CDs and other goods.
More than 13,000 people nationwide have died since President Felipe Calderon launched a war on the drug cartels in December 2006. Though lawyers -- along with prosecutors and judges -- represent a small percentage of that toll, attacks on them underscore the ability of the cartels to strike back at the judiciary system.
The risks inspire a cloak-and-dagger existence for major-league drug lawyers. A Sinaloa attorney who handles big-time drug cases asked a pair of Times journalists to turn off their cellphones during a meeting at a restaurant in Culiacan recently, fearing an active line might steer enemies to his location. Two associates sat watch as he discussed his work on condition that neither he nor his clients be identified.
The lawyer, from a poorer part of Mexico, moved to Culiacan to attend college, and, following law school, began with nickel-and-dime cases in the local courts. After a few victories, he caught the eye of drug-cartel representatives and accepted their offer of work.
He exudes nervous energy -- pacing, whispering into one of his three cellphones, giving away little about where he is going or who he will see.
Drug clients, like his, bring in the kind of handsome fees that can pay for top-shelf office space in Culiacan's pricey Old Town section. But they also play havoc with a lawyer's nerves, often ignoring his best legal advice while making it clear that there is no option but to win.
"If they think you have done them wrong, it's . . . " the attorney said. He finished by drawing his finger across his throat.