Since 1993, Juarez officials have counted more than 180 unexplained slayings of young women in the desert scrub surrounding the murky Rio Grande. Many have been raped, strangled, then ritually stabbed. Dozens of corpses were found with the right breast hacked off and bitemarks bruising the left.
Other bodies, after long exposure to the elements, are less gruesome but much more difficult to identify. Ms Chavez organises volunteers to scour the wastelands for the young women's remains, even though the authorities say the brute responsible has been behind bars for nearly four years.
"It frightens me to think it may be more than one killer," said Lilia Quintana, a Juarez social worker, who helps to counsel thousands of girls who work night shifts in Juarez's 350 factories for subsistence wages.
Abdel Latif Sharif, a chemical engineer born in Egypt, initially was charged with 17 murders of local women. Police staked out many strip joints and noticed a tough regular, nicknamed El Narco, who proved to be on the run from sexual assault charges in Florida. Yet there has been no let- up in the killings since Sharif was locked up in Cereso jail - then transferred to a high-security prison in Mexico City, convicted of killing a bar girl in 1993.
Sharif periodically denounces officials for concocting sensational cases against him for political mileage, and he ridiculed the latest twist in the tale: the police's account that he had paid four cocaine- addicted bus drivers to kill twice a month, and arranged for a go-between to bring back press clippings and the victims' knickers before collecting a $1,200 (pounds 750) bounty, was "something out of a movie", Sharif told reporters. "This protects the real murderer. It has got to be someone with plenty of money and influence."
Two months ago one attack brought the first eye-witness to Juarez's rapes and killings. A 14-year-old called Nancy was raped, throttled and left for dead after work. But, against all odds, she survived and later identified her assailant as her usual bus driver, Jesus Manuel Guardado Marquez. He is now in jail awaiting trial for rape, strangulation and attempted murder.
Feminists fear that in a notorious vice spot such as Juarez, where gang and drug killings matter more than missing factory girls, violence is endemic.
Last year, Juarez politicians invited criminal profilers from the United States Federal Bureau of Investigation to help. Robert Ressler, the model for the special agent who was Hannibal Lecter's nemesis in the film Silence of the Lambs, came twice. He said that one-third of these murders shared a pattern. "There is a perception of some wildman... but this is not entirely correct. Out of 76 homicides in question, the bodies were found in three sites."
Mr Ressler doubts that the killers are Mexican. "There is a strong possibility of American involvement - whether a single killer, a duo, or a team coming across. Juarez is a serial killer's dream because it reels so many young women into its factories," he said.
The women now travel in groups. Plastic whistles have been issued, and pepper sprays. But none of this brings security. "Somehow we must cope with a waking nightmare," Ms Chavez said. "We cannot sleep."