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.