Blow-by-blow: How the terrifying Moscow ISIS terror attack that killed 143 people unfolded as music fans waited to hear their favourite band

Bullet after bullet tore through hundreds of unsuspecting music fans in Moscow on Friday night, all of whom had trekked to the western outskirts of Russia's capital to sing their hearts out. 

The ISIS attack, carried out by one of the terror group's most violent sects, saw four armed and dangerous men slaughter innocent civilians who were settling down to watch Russian rock band Picnic perform at the Crocus City Hall venue on March 22. 

But the concert didn't even get to begin before four terrorists who belonged to an ultra-violent sect of the terror group began shooting at innocent civilians. 

Details of exactly what happened on Friday night are slowly emerging, and Russia investigators are slowly piecing the attack together. 

Here, MailOnline looks at exactly what happened on that terrible night.  

A clip shows a terrorist running through security gates at the concert hall

Rescuers clearing the rubble and extinguishing fires in the hall of the Crocus City Hall

The men were seen arriving in a white, unmarked van shortly before the attack. 

Witnesses to the attack, whose words were backed up by video footage shared to social media, told media outlets that the four-man group started shooting automatic Kalashnikovs as they entered the foyer of the venue. 

They made their way into venue just before 8pm on Friday, sweeping across the lobby and taking potshots at people waiting in the foyer. 

The four terrorists all worked for ISIS-K, an offshoot of ISIS that is known for its barbarity that was set up in late 2014 in eastern Afghanistan in the wake of US-led airstrikes against ISIS strongholds across Iraq. 

The group has been led by Shahab al-Muhajir, an engineer by training and education, since 2020.

His name means 'Shahab the Migrant', referring to the fact that he is the first non-Afghan and non-Pakistani person to run ISIS-K. 

More and more gunshots rang through the lobby as the terrorists continued to slaughter innocent people while they walked through the lobby. 

The fire consumed much of the building

Crocus City Hall is located in the city's Krasnogorsk Urban Settlement in the Krasnogorsky District

Bodies were seen in footage shared to social media falling one after the other as the terrorists made their way to the concert hall area. 

Inside, concertgoers started to panic and head towards the exits. But they were forced to duck for cover as the ISIS gunmen began wildly firing into the gathered crowd. 

One terrorist then started a fire that would consume much of the building. Witnesses said they saw at least of them dousing seats in a liquid before igniting it. 

Russian news reports cited authorities and witnesses as saying the attackers threw explosive devices that started the fire, which eventually consumed the building and caused its roof to collapse.

Dave Primov, who survived the attack, told the AP that the gunmen were 'shooting directly into the crowd of people who were in the front rows'.

He described the chaos in the hall as concertgoers rushed to leave the building: 'People began to panic, started to run and collided with each other. Some fell down and others trampled on them.'

The large venue was engulfed in flames after at least five armed men in camouflage stormed the hall 

Pictured: Hundreds of people get up from their seats and head for the exits as gunshots are heard at the concert hall

After he and others crawled out of the hall into nearby utility rooms, he said he heard pops from small explosives and smelled burning as the attackers set the building ablaze.

By the time they got out of the massive building 25 minutes later, it was engulfed in flames.

'Had it been just a little longer, we could simply get stuck there in the fire,' Mr Primov said.

Another at the scene hours after the attack saw black smoke and flames coming from the roof of the concert hall, which can hold up to 6,000 people. Helicopters sought to douse flames that engulfed the large building.

Eventually, emergency services were able to get in and treat the injured and authorities were able to begin their investigation into exaclty what happened.   

Investigators said some died from gunshot wounds and others in a huge fire that broke out in the complex. Reports said the gunmen lit the blaze using petrol from canisters they carried in rucksacks.

The hall, which is still ablaze, has a capacity of 6,000 spectators

Seventy ambulances have attended the scene of the building engulfed in flames

Gunmen have targeted a concert hall in a mass shooting in Moscow 

People fled in panic. Baza, a news outlet with good contacts in Russian security and law enforcement, said 28 bodies were found in a toilet and 14 on a staircase. 'Many mothers were found embracing their children,' it said.

Investigators on Saturday were combing through the charred wreckage of the hall for more victims, and authorities said the death toll could still rise.  

US intelligence officials strongly believe that members of Islamic State in Khorasan Province, or ISIS-K, that carried out the attack. Tonight, the US officially rebutted Vladimir Putin's claims that the attacks were carried out on Ukraine's orders. 

'ISIS bears sole responsibility for this attack. There was no Ukrainian involvement whatsoever,' National Security Council spokeswoman Adrienne Watson said in a statement.

ISIS-K, set up in late 2014 in eastern Afghanistan in the wake of US-led airstrikes against ISIS strongholds across Iraq, is known for its extreme brutality.