The murder spree began in June, the letter indicates. It says Iqbal sometimes killed two or three boys on the same day, with the help of unknown accomplices. When police entered his dark, dilapidated three-room house, they found bags of shoes and garments, as well as two skeletons floating in vats of sulfuric and hydrochloric acid. Confessional statements were tacked to the stained and mildewed walls.

As word of the killings spread, hundreds of distraught parents came to Lahore's Ravi Road police station to sift through heaps of children's clothing and rubber sandals dumped in the courtyard. They also studied pictures taken of the victims before they died. The boys, aged 9 to 18, are shown in Iqbal's house. Some are smiling uncertainly, others look tough and serious. Haleema Bibi's son is grinning brightly. On the back of the photo, the boy's name, father's name, residence and date of death are noted. Also a number: victim 39. So far, relatives have identified the clothing and snapshots of 72 boys, although the remains of only a few have been found.

The killings, commentators say, are part of the price Pakistan is paying as it stumbles toward modernity. The country has experienced a dramatic loss of innocence in the past 15 years, particularly in the wake of the Afghanistan wars, which left Pakistan awash with guns and heroin. But this incident may also reflect a modern malaise in one of the world's most rapidly urbanizing countries. Since 1981, Lahore's population has more than doubled to about 7 million, and services have not kept pace. "The demographic pressures have broken traditional safety nets," says Islamabad anthropologist Adam Nayyar. Inflation, unemployment and poverty are all at high levels. Almost half of Pakistan's 130 million people are under age 18, according to UNICEF, and more and more young people from poor families are left to fend for themselves. "People are exploiting those kids now," says Dr. Ambreen Ahmed, a child psychiatrist in Islamabad. "No one knows to whom they belong. As cities become bigger, people lose track."

One disturbing question is why parents of only 25 of the boys bothered to report them missing. Perhaps that's because many Pakistanis distrust their corrupt and abusive police, so the parents may have felt they had nowhere to turn. "It never occurred to me to go to the police for help," says Haleema Bibi. Iqbal had been known locally for his interest in young boys, and three arrests for molesting failed to change his behavior. Neighbors tried to keep him in check by forcing him to make humiliating public apologies. Iqbal simply moved to another part of town where he could be anonymous. None of his latest neighbors noticed anything unusual.

Despite reward offers, police have been unable to find Iqbal, and there's no proof he actually killed himself. That he has eluded arrest is especially disturbing to families of the dead boys. Says Shamim Akhtar, whose son Kamran Shaukat, 14, was one of the victims: "Nobody knows the pain I am going through. Because we are poor, nothing is being done."

With reporting by Ghulam Hasnain/Lahore