The girl, whom authorities have described as mentally challenged, now sits in jail in Rawalpindi, charged by police with blasphemy, while her family has been put in federal protective custody. The evidence against her is muddled at best, but police said they arrested her in part to assuage the mob and also because they knew she would be safer in jail.
"The one who burned the Koran should be burned," said Shaukhat Ali, an assistant at the local mosque, expressing a sentiment shared by many Muslims in the community.
Under Pakistani law, those found guilty of defaming the Islamic prophet Muhammad face the death penalty, while defiling the Koran can bring a life sentence. The case of the girl is the fourth in recent months to alarm human rights advocates, who say the law is frequently used to persecute Christians and also has been unfairly applied to the mentally ill - including some Muslims.
Liberal-to-moderate Pakistanis see the rise in blasphemy allegations as a reflection of a dangerous ascent of extremism and anti-Western sentiment throughout society.
"Most of the people consider the Christians here to represent the West," said Paul Bhatti, who heads the Ministry of National Harmony - a post created after his younger brother, Shahbaz Bhatti, a Catholic and minority affairs minister, was assassinated by the Pakistani Taliban last year for advocating reform of the blasphemy laws.
Shahbaz Bhatti was the second prominent politician killed in 2011 for his opposition to the laws: Salman Taseer, the governor of Punjab Province, was gunned down by a member of his security retinue who immediately confessed and was widely celebrated in Pakistan for defending Islam.
Christians are easy targets for false claims by accusers with ulterior motives. Pakistani President Asif Ali Zardari took "serious note" of the girl's arrest, a spokesman said Sunday, and quoted him as saying, "Blasphemy by anyone cannot be condoned, but no one will be allowed to misuse blasphemy law for settling personal scores."
In an interview Sunday night at his heavily guarded office in Islamabad, Bhatti said such allegations are usually leveled against the poor and the powerless. The 50-year-old physician said he has drawn no firm conclusions about the girl's case, but knows one thing: Even if cleared, she and her family can never return to their home.
"If she is not guilty, some can understand and they can forgive," he said. "But there are people who just want to have death."
The slum where the 12-year-old lived is typical of other desperately poor Christian enclaves in and around the comparatively prosperous capital. Many Christians live in lean-tos and toil as trash pickers or wood scavengers.
The incident involving the girl happened Thursday afternoon, evidently while she was gathering trash - but beyond that, everything is in dispute. Some locals claim to have witnessed her and her mother burning the entire Koran.
But Tahir Muhammad, a 30-year-old shop owner and landlord, said the girl found just one page of the holy book while cleaning a house, mixed it with other papers and burned it.
A 10-year-old neighborhood girl said she saw the whole thing and took the ashes to the mosque - with no pages of the Koran extant. In interviews Sunday, two men at the mosque also said only ashes remained and that the imam mixed in some pages himself before turning over the "evidence" to police.
"Somebody must be confused when they said pages were mixed in no such thing happened," Imam Hafiz Muhammad Zubair said Monday. He also said community leaders decided to turn the girl and her mother over to police for their safety.
"Both the women confessed to us that they had indeed burned the Koran," he said.
Various tellings of the incident spread Friday to other mosques. Some outside religious leaders and locals encouraged Muslims to converge on the Christian enclave, but others counseled restraint, said Bhatti, who talked with several clerics.
An estimated 500 to 1,000 Muslims, including many outsiders, turned out Friday to demand punishment for the alleged blasphemer, blocking a nearby highway and burning tires. The mob also menaced the police.
Other Muslims, who said they count Christians as their friends, said they oppose vigilantism. However, in their view, if the girl is found guilty then the Christians must leave for good.
"The people here are not extremists," said Asad Riaz, 30, sitting in the mosque Sunday evening, "but this has provoked them."
The imam sounded a note of conciliation, but with conditions. "It isn't really those poor folks' fault," Zubair said, "but we will wait and see what the official verdict against her is - and if they are guilty then decide accordingly."
Over the weekend, residents of the Christian enclave began to migrate to other colonies in Islamabad, where they have remained. Authorities said they could not guarantee their safety if they return.
Some Christians who stayed in the area said shopkeepers are refusing to sell them food and have issued threats.
"They said they will burn our house down if we don't leave," said 17-year-old Adnan, who lived next to the accused girl's family. "They are also saying that since a woman burned the Koran they will come after our women now."
He and his cousin, perched nervously on a motorbike, would soon be migrating to Islamabad, too, they said, then took off into the night.