Sweepers start to clear away debris, and drills buzz in the shells of gutted shops.

But the scene of the deadliest ever attack carried out by so-called Islamic State (IS) anywhere in the world is still a makeshift shrine. On 3 July, 292 Iraqis lost their lives here.

This week, the haunting strains of a cello wafted through the cavernous black hulks where two popular centres once drew in Iraqis for shopping and socialising.

"If terrorists are trying to turn every element of life into a battlefield, I will turn it into a field of beauty and civilisation," declares Karim Wasifi, composer and conductor with Iraq's National Symphony Orchestra.

He has played his cello at other major bomb sites in Baghdad as an affirmation of Iraqis' determination to fight back

Hardly a day goes by without an attack somewhere in a city laced with security checkpoints and armed guards.

But the explosion in Baghdad's Karrada neighbourhood was no ordinary bomb. From its design to its destination, this attack underlines that IS has found a new way to inflict harm and cause terror.

"Daesh used, for the first time, a new tactic which helped it to move undetected through checkpoints," a Western security source in Baghdad tells me, using the name for IS more commonly used in the region.

"We've never seen it before, and it's very worrying."

'Unique' chemical mix

Precise details of the attack, which is under Iraqi investigation, are still being pieced together.

The tactic known as a VBIED - vehicle-borne improvised explosive device - is now widely used in suicide bombings.

But this one is said to differ in the way the explosives were placed in the van, and how the chemicals were put together.

"It's really difficult to make," an explosives expert who has knowledge of the investigation explained, saying the device may have been developed in the Iraqi city of Falluja when it was under IS control.

"Daesh has given a lot of thought to how to move through checkpoints."

The bomb-makers are believed to have taken a formula "available on the internet", and then adjusted the quantities to reduce its risk of detection, and increase its impact.

Several Iraqi experts also described the mix of chemicals as "unique".

"We are used to big fires but the chemicals in this bomb were used for the first time in Iraq," says Brigadier General Kadhim Bashir Saleh of the Civil Defense Force.

"It was unique, strange, and terrible."

Another Iraqi security expert, Hisham al-Hashimi, told me he believes a similar mix of explosives may have been used, only once, in an attack by al-Qaeda in 2004.

But he describes this new tactic deployed by IS as "very serious and dangerous".

The van exploded on the narrow street just after midnight shortly before Eid Festival when shops were packed with families, football fans were glued to big screens, and the billiard hall was doing brisk business.

Several say the heat created by the first blast was "as hot as the surface of the sun".

The explosion left no gaping crater, and its impact did not wreck the nearest buildings.

But it set off secondary fires which turned out to be the most deadly of all.

No fire escapes

Their devastating impact was then multiplied by a series of safety failures.

"There were no fire escapes," laments Sadiq Maroof, a shopkeeper who was one of a small number of people who escaped alive.

He takes me through the skeletal remains of the Laith Centre, from the blackened basement where he once ran two popular clothing shops, to the second floor room where he fled for his life.

"The stairs behind me were on fire so we pulled a window out of its frame and jumped."

"There had been two escapes," he says, still visibly angry and upset. This tragedy took the lives of nine people from his own family and many close friends.

"The first floor exit had been turned into a shop and the second floor escape became a storage room."

Several experts estimated the initial bomb would have killed 20-30 people. The ensuing inferno then trapped many inside.

"The absence of fire escapes and safety regulations caused the highest number of casualties," says retired Brigadier General Khalaf Abdul Karim who was at the scene that night.

"We could hear people trapped inside desperately calling their family and friends for help. In those minutes some could have been saved."

The fire tore through shops with cheap styrofoam walls and bad wiring, with perfumes and other goods fuelling the flames.

Each time we went to the street, grieving relatives approached us with harsh words for their emergency services, accusing them of arriving too late, and of not doing enough.

When I ask Chief Sergeant Habib Dewan about the accusations, he immediately bursts into tears.

"We normally reach the scene in 4-5 minutes but we reached it in 8- 10 minutes," the fireman says.

"I've never seen anything like it," he says of the blazing orange fireball which engulfed the entire street.

"We were ready to jump into the fire to save people. We did everything we could but this was an over-whelming attack."

There are many Iraqi stories about how a van was able to enter a street only used for pedestrian traffic.

Some versions speak of a driver carrying official badges, others of the complicity of the security guards at the nearest checkpoints.

But this biggest single attack on civilians since the Iraq war of 2003 has finally focused official attention on the widespread use of detector "wands" which were proven long ago to be fake.

In the wake of this bombing, Prime Minister Haider al-Abadi finally ordered their removal from checkpoints.

"Well - trained sniffer dogs are what's needed to stop these devices " says one explosives expert in Baghdad.

Security experts say even IS may not have expected to inflict such a high number of casualties in their Karrada bombing. "They got lucky," is how one put it.

But life was pulled out of a Baghdad neighbourhood which still mourns its great loss