It’s not an easy point to make in Duque de Caxias, perhaps the most violent of the sprawling suburbs on the tattered northern outskirts of Rio de Janeiro. Despite a crackdown, death squads still prowl there. Hiring a hit man can cost as little as $33. Convictions are hard to get because exterminators rarely leave witnesses; without a witness-protection program, those who do survive often clam up in court. To nail Antonio Camilo de Lima, a security guard allegedly hired to exterminate four young men, Tania Maria had to rely on the pretrial deposition of two who survived the initial attack. (By the time the case came to trial, one of the survivors had died and the other had vanished.)

Most often, she must weave her case out of the few threads of circumstantial evidence. Tania Maria spends months digging up prior arrests, old depositions and relatives connected to various crimes" good old archive work," as she puts it. After a two-year investigation and the help of a special legislative commission, she recently won a case against Tiao da Mineira, a reputed local exterminator who was sentenced to 18 years in prison-not for killing children but for murdering his wife in a domestic brawl. Her main task in the courtroom was to unmask the defendant, who called on his entire family to testify. Dressed in her formal black robe and red satin sash, she savaged Tiao’s claim of innocence. “Most of these guys come off as saints before the jury,” she says. “[But] no one in his right mind would break into the house of Tiao da Mineira, a known killer, and murder his wife.”

It’s one thing to deal with a miserably equipped police force and a forensic process so primitive that medical examiners must sometimes let a corpse disintegrate to find the bullets. Betrayal at the hands of a colleague is quite another. Last year a fellow state’s attorney–the only other lawyer in Brazil devoted exclusively to these cases-suddenly interrupted a trial to ask the jury to acquit the man he was prosecuting: Pedro Capeta, a businessman accused of several murders. Capeta walked; the prosecutor eventually resigned, leaving behind a stack of new cases but not a word of explanation as to his sudden change of heart. Tania Maria pushes on, despite repeated death threats, which have forced her to walk day and night with two bodyguards. “The big-time killers, the ones who mastermind these murders, are still free,” she laments. Bagging them won’t be easy. But Tania Maria is the best hope the children have.