The Agha family are scared of the "agencies" - a sweeping phrase that covers everyone from the Pakistani Rangers to the many intelligence groups brought into Karachi by the Prime Minister, Benazir Bhutto, to halt the city's spiral into anarchy. The boy and his sisters (whom relatives asked not be identified) should be witnesses in the state's case against terrorists but they are on the run.
Late on the night of 19 February, 12 gunmen, some of whom the boy recognised, broke into the house. The boy dived under a bed and watched as one of the intruders hacked his brother with a butcher's knife, cursing him for belonging to the Shia stream of Islam. Then his four brothers were shot dead.
The killers had pushed his three sisters into another room and locked the door, not knowing there was a telephone inside. For more than 30 minutes, while the assassins were torturing one of the brothers, one girl tried dialling the police emergency number. It rang and rang, but nobody bothered to answer. Such is Karachi these days.
This neighbourhood is mainly Shia, and when people were roused by the gunfire, a wave of anger spread through the crowd. Some thought the killings might have been the work of Sunni Muslim extremists. There is a large Sunni community across the main road in number 17 block. But for the past decade the two Muslim faiths have lived harmoniously.
Then the boy was found, in shock, under the bed. He was taken to the police station where he identified two of the killers. But, according to the boy, they were not Sunni fanatics. They belonged to an armed faction known as Haqiqi, which was initially set up by the Pakistani army to split the Mohajir Qaumi Movement (MQM), which represents the millions of Indian Muslims who migrated to Pakistan after the 1947 partition.
As with other attempts by the military to manipulate events with guns and money, the results were not always what they expected. The Mohajirs were promised "an Islamic homeland". Instead, they are often despised as trespassers by the feudal families, among them Ms Bhutto's, that still run Pakistan.
Nowhere is this hostility more acute than in Karachi, where the Indian migrants comprise more than 60 per cent of the city's 12 million population. The MQM and Ms Bhutto's supporters fought pitched battles for control of the city, forcing the army to intervene. When they withdrew in 1992, control of the Haqiqi faction was passed on to one or several of the country's six intelligence agencies. Police arrested 12 suspects, all reportedly Haqiqi members. All were wanted in previous cases of murder, car theft and extortion.
The police superintendent in charge of the case was then ordered by the Rangers' chief to release the suspects and tear up the charges. The police officer refused, and when Shia clergymen were alerted that the Rangers were setting loose the suspected killers, the mullahs in protest refused to bury the four brothers.
Fearing religious riots, the authorities went ahead with the arrests, just long enough for the bodies to be buried. Then the Haqiqi members were released. The superintendent was transferred, as was the magistrate who issued the arrest order.
The boy, his sisters and a brother-in-law, according to a family friend, were told by the Rangers to drop charges or else "their family would be smashed".
Interviews with many Muslim leaders and witnesses of three "sectarian" killings in Karachi show there is scant evidence that rival gangs from the Sunni and Shia communities are causing the bloodshed. After a bomb blast in a Shia mosque recently, hundreds of Sunni volunteers gave blood to the injured and helped to shoulder the coffins of the many dead worshippers.
What does seem undeniable is that many of the murders in Karachi - with targets selected to turn the Sunnis and Shias against each other - were carried out by Haqiqi gunmen. American and Pakistani detectives trying to hunt the assassins of two American diplomats killed on 8 March also are investigating the possibility that Haqiqi was involved.
It is not clear whether the Haqiqi have ganged up with a Sunni extremist group, known as the Soldiers of the Companions of the Prophet, to polarise the Mohajir community, robbing the non-sectarian MQM of its support. Another equally ominous possibility is that the Haqiqi, said to number more than 500 gunmen, are still being run by a renegade intelligence agency out to sabotage Ms Bhutto's government.
Pakistani businessmen are calling a nationwide strike today and demanding that Ms Bhutto send the army into Karachi. Many feel this is a mistake, as it was the army that created, trained and armed the Haqiqi killers, in the first place.