Captain Harith al-Sudani, a mole from Iraq's little-known Falcon Intelligence Cell

On a day when four bombs had already rocked Baghdad a car parked up in a back street, laden with explosives ready to cause more carnage.

Soon afterwards, thick black smoke rose skywards and victims lay scattered on the floor. Some looked dead, others injured, screaming for help as they clung to life.

To any locals who stumbled across the scene, it was one of sheer horror.

But all was not as it seemed. For when the car exploded the street was empty. Only after the device detonated did the 'wounded' run in, taking up their positions like well-trained actors.

The payload of the original bomb had been replaced by a much smaller device, designed to deceive rather than destroy.

The ruse was the work of Captain Harith al-Sudani, a mole from Iraq's little-known Falcon Intelligence Cell, who managed to penetrate the highest ranks of Islamic State.

When the footage was taken in 2016, he was 14 months into one of the world's most dangerous undercover operations.

As he posed as a jihadi, his job with the terror group was to transport bombs to specific targets before detonating them.

But in reality, the father of three was handing them over for his team to disable, and then faking explosions and casualties so that IS leaders believed their sick plots had succeeded.

After the bomb went off in the Al-Hurriyah district of north-west Baghdad, Iraqi police issued a statement saying at least ten victims had been killed and 34 wounded. They said the attack had targeted a popular fruit and vegetable market in a commercial street.

Thinking that a murderous terrorist plot had been carried out as planned, the IS-linked Amaq News Agency laid claim to the bombing.

But the 'attack' – including the arrival of the fake victims – had been caught on CCTV from a neighbouring building, and the footage subsequently leaked. Security officials shut down rumours of a hoax, with some claiming the scene was actually a film set.

It is only now, with the heroic double-agent dead and IS near-defeated on the battlefield, that the truth can be revealed.

Captain al-Sudani is believed to be one of the blindfolded men shot by IS in this video from 2017

Captain al-Sudani, considered one of Iraq's greatest spies, foiled 30 vehicle-explosion attacks and prevented 18 suicide bombings.

His father Abid, said of his son's bravery: 'He saved the lives of many people. He wanted to serve his country.

'Every operation was stopping the bloodshed of innocents. Let his work tell the story.'

Weeks after the car bomb was caught on camera, 36-year-old Captain al-Sudani, a former computer technician, sent his father a text on New Year's Eve.

'Pray for me,' he wrote, as he set out on what was to be his penultimate mission in the markets of eastern Baghdad.

CCTV footage in a street in Al-Hurriyah, Baghdad, from 2016 shows a man parking a car (left), before walking away and getting into a truck (right) that drives away

The spy had 1,100 pounds of military-grade explosives in his truck.

He was sweating, as any slight bump from one of Baghdad's notoriously bad drivers could set off the bomb.

He also feared that his carefully maintained cover may have been blown. He was told he had been chosen to take part in a spectacular attack, which would see a series of co-ordinated bombings in multiple cities across the world. He picked up a white Kia truck-bomb in the eastern Baghdad neighbourhood of Al-Khadra and set off towards his target. His Falcon team were on standby to intercept the truck packed with explosives.

But on the way to meet them at a safe rendezvous point, his jihadi handler called him from Mosul and accused him of lying about where he was.

In a moment's panic, Captain al-Sudani said he must have made a wrong turn, which the IS commander appeared to accept.

The spy then called his comrades and told them the plan had to change – and they should meet him nearer to the planned attack site.

After the truck explodes in the empty street, injuring no one, fake ‘victims’ arrive and lie down on the ground among the shrapnel, pretending to be in pain

Springing into action as soon as the Captain pulled up, eight agents dismantled the bomb, removing the electronic detonator, 26 plastic bags of C4 and ball bearings.

In another clever ruse Iraqi security officials planted a story with the Arabic media, who told of a white truck exploding outside the Al-Bayda cinema in eastern Baghdad. The IS mission was seen as a success.

But what Captain al-Sudani did not know was that his terrorist masters had bugged his truck – and so they heard his entire conversation with the Falcons.

The intelligence agency's director, Abu Ali al-Basri, told the Daily Mail: 'When Daesh [the Arabic name for IS] had some doubt about him, they provided him with a truck bomb. It was supposed to be blown up in a market area. Daesh planted a spying device in his car and they listened to his conversations.'

In January 2017, after 16 months undercover, Captain al-Sudani received what would be his final mission.

This time he was ordered to a remote farmhouse outside Tarmiya, north of Baghdad, then an IS stronghold. He entered the building and never came out.

As more actors arrive, one man starts to load ‘casualties’ into his van. Islamic State believed that its ‘attack’ had been successful

A member of his unit, who asked not to be named, said of the mission: 'We were waiting for him and preparing another fake car bomb, to deceive [IS] and protect people from their evil, but Harith never came back.

'We waited for four days for the green light to break in [to the farmhouse] and search for him.'

They were eventually given the order to mount a rescue operation. One Iraqi officer was killed in the raid, but there was no sign of Captain al-Sudani.

Footage released by IS in August 2017 shows the moment that Iraqi intelligence officers believe he was executed. It is not known how long he was held captive, although it is likely he was tortured. Captain al-Sudani is thought to be one of the four prisoners, blindfolded and wearing orange jumpsuits, seen being shot in a wooded area in the IS propaganda video.

His former Falcon team-mate said he would never be forgotten. 'Harith managed to infiltrate Daesh for two years, and he lived among them and saved [the] lives of innocent people,' they said.

'In one week he gave information about 11 suicide bombers, with accurate details which led to them being killed. Daesh did not suspect him [at the time].'

Mr al-Basri said: 'He was giving us all the information about the car bombs and the locations Daesh wanted to strike.

'We defused the bombs and made fake bombs in the locations to give messages that [attacks were] achieved.'

It was not until after Captain al-Sudani's death that his wife, Raghad Chaloob, and their children learned of his secret life.

His 12-year-old son, Moamal, told a local TV channel earlier this month: 'My dad was spending most of his time in his work. We asked him to stay at home with us, but he was saying 'I can't, our country is more important'.

'He joined Daesh to ruin their plots. We are very proud of him.'

The Falcon Intelligence Cell works with British Special Forces as it continues to hunt down jihadis. It is instrumental in the search for the terror group's leaders as IS loses control of its last remaining pockets of territory.

Additional reporting: Ammar Shamary