By Soutik Biswas
BBC News, Kabul
The bullet-proof car carrying Ali Shah Paktiwal, the head of Kabul police's criminal branch, was about to turn into the street from the drab police headquarters building when it suddenly shook and rose in the dusty air before landing with a thud.
The blast was heard far across the city
"I asked my driver what was happening," says Mr Paktiwal, barely three hours after the incident. "Why was the car shaking and moving up and down? I didn't hear any sound."
A few hundred metres away, on the narrow road, a bus carrying Afghan police instructors had been blown up, sending flames and clouds of dust up into the sky.
The blast also ripped through two other vehicles - a civilian bus and a small van. There was blood, and shards of glass and shrapnel flying. Civilians milling around in the busy street overlooking the city's brown mountains had been caught up in the explosion as well.
At the end of another episode of violence in the country's bloody history - and what was probably the biggest carnage in Kabul since the fall of the Taleban - up to 35 people, mostly police instructors, had died.
The wounded included Japanese, Korean and Pakistani nationals and two Afghan women, both civilians who were walking past the bus.
Across the street, in the police headquarters, officials were busy looking for evidence to determine whether the devastation was the result of a suicide attack or timed explosives placed in the bus before it began its journey.
A large crowd watched the scene from across the wide road. Many speculated that this was the latest in a series of suicide attacks that has rocked Kabul and surrounding areas in the past few days.
But intelligence officials told the BBC that early leads hinted at sophisticated timed explosives in the police bus rather than a suicide attack.
"The range of destruction is too wide," said an official who preferred to remain unnamed.
"A suicide attacker would need to pack a huge amount of explosives on him to destroy three buses and kill 35 people. It doesn't make sense."
Outside, in the gardens of the police headquarters, Kabul police chief Ismatullah Dawlatzai was repeating what is becoming a rather tiresome explanation for Kabul's residents.
"The explosion was the work of people who are enemies of Afghanistan, its people and of Islam," he told reporters.
"They are being exported to the country from outside."
'Nowhere is safe'
Such talk does not placate the locals - many people watching the scene of destruction and stranded in the middle of the city cursed the government, and the lack of security.
"The thing is that if they can put explosives inside a police bus, they can put them anywhere," said Sattar, who works in a mobile phone shop and was on his way to work.
The police bus was completely wrecked by the blast
"Nobody's life is safe here."
Shop-owner Haji Mohammed Gul echoed the same sentiment.
"I am very scared. All this affects our lives and businesses," he said.
Another man in the crowd shouted that the violence would only stop when the foreign forces left the country.
"They have brought this curse upon us," he shouted before melting into the crowd.
Back in his office, I asked Mr Paktiwal whether this was his closest brush with death in his job.
"No, no, there have been closer ones, and more dangerous too," he said.