The attack, which came in the middle of a busy Saturday afternoon, was the third terrorist incident to hit Turkey's biggest city in a week. Witnesses said three people drew up in a car, threw petrol bombs into the ground floor of the modern building in the Goztepe district on the Asian side of the Bosphorus, and fled the scene on foot, pursued by a policeman.
The blaze swept rapidly upwards and engulfed the five-storey building, shattering windows and driving shoppers up staircases in search of safety. Lives might have been saved if the first fire engine on the scene had had a ladder; according to fire service radio, 10 of the bodies were found in the attic.
People watched helplessly below on the crowded street. "The whole building became like one enormous flame," said a young boy. "Everyone ran up the stairs to the top and they were screaming for help."
According to Istanbul's fire chief, Sabri Yalin, "the assailants forced people upstairs with their guns, poured petrol in the building and set it on fire". Most of the victims died of smoke inhalation, said Mr Yalin, adding: "If there had been a fire escape no one would have died. Those who licensed this building should be investigated." President Suleyman Demirel condemned the attack as "insidious" and the Prime Minister, Bulent Ecevit, said it was part of a campaign to disrupt national elections on 18 April.
As night fell, fire fighters were still working on the roof of the store. So intense was the blaze that the steel frame of the building was laid bare and trees on the street outside were charred black. In ground floor display windows, only red "Sale" signs and a grotesque tangle of dummies survived. A foul stench enveloped the area.
An angry crowd outside was in no doubt about who was responsible, chanting "Death to the PKK". The Kurdish Workers Party (PKK), which wants autonomy for Kurds in south-east Turkey, was always going to be the prime suspect - it warned it would step up its campaign of terror after its leader, Abdullah Ocalan, was snatched from Kenya by Turkish special forces last month. Mr Ocalan is awaiting trial in a Turkish jail.
Turkey, however, has no shortage of groups willing to resort to terror. Both Kurdish extremists claiming disaffection with the PKK, and an extreme Marxist group, claimed responsibility for bomb attacks in Istanbul earlier in the week.
Terrorism is nothing new to Turkey, but the recent spate of incidents in Istanbul, which is a large tourist centre, is bound to cause alarm. "We're afraid," said a bystander as fire fighters put out the last of the blaze yesterday. "Everybody's afraid of terrorism."