I didn’t think I could ever feel angrier than I did on Tuesday when I first heard an ISIS suicide bomber had deliberately targeted, murdered and maimed young girls as they left a pop concert.

It’s impossible to imagine a more heinous, sickening and pathetically cowardly act on so many vulnerable, innocent and defenceless people.

Yet today my initial rage has manifested into cold fury and revulsion that the medieval barbarian who committed this atrocity wasn’t stopped long before he ever had the chance to detonate his death and destruction.

Salman Abedi (pictured left and right) was known to authorities had only just returned from war-torn Libya before launching his horrific attack in Manchester Arena

It’s not unusual after these terror attacks for details to emerge from the perpetrator’s background that should have sparked red flags of concern.

But in Manchester killer Salman Abedi’s case, there were so many red flags it’s an incomprehensible scandal how he was able to evade detection and apprehension.

Short of this loathsome monster standing on the roof of his house waving an ISIS flag and screaming ‘Death to the infidels!’, I’m not sure what more Abedi could have done to self-identify as a would-be terrorist.

His parents are Libyan-born refugees who fled to the UK to escape dictator Muammar Gaddafi. They returned after Gaddafi was overthrown in 2011, leaving Abedi with siblings in Manchester.

For a while, he was a normal happy young kid who supported Manchester United, drank and smoked weed at parties, and who studied hard to win a place on a business course at Greater Manchester’s Salford University.

Then two years ago, everything suddenly changed.

Abedi began travelling more often to Libya, where ISIS and Al-Qaeda are known to have numerous training camps and where his own father was linked to the militant Libyan Islamic Fighting Group.

Pictures, first published by the New York Times, show the remnants of the backpack bomb terrorist Salman Abedi used to kill at least 22 people as they left an Ariana Grande concert on Monday night

He dropped out of University.

He began to dress in long Islamic robes.

He grew a beard.

He stopped drinking alcohol.

He fell off public radar, shunning the social life he once so enthusiastically enjoyed and appearing more often at his local Didsbury Mosque.

He became withdrawn and angry.

Around this time in 2015, Mohammed Saeed, an imam at the mosque, delivered a sermon attacking ISIS.

Abedi didn’t like what he heard.

‘Salman showed me a face of hate after that sermon,’ said Saeed this week, adding ‘it’s not a surprise to me’ that he carried out the attack.

The leaked photos show the remains of a small handheld detonator used to explode the bomb, which contained nails, nuts and bolts

Akram Ramadan, a member of south Manchester’s large Libyan community, claimed Abedi was subsequently banned from the mosque for the incident. ‘He told the Imam “you’re talking b*****s” and he gave a good stare, a threatening stare right into the Imam’s eyes.’

Ramadan also claimed the mosque reported him to Home Office’s Prevent anti-radicalisation programme.

Family friend Adel Elghrani disclosed that Abedi’s parents became so worried about his behaviour they ordered him to leave the UK and live with them in Libya.

He said: ‘The father was so concerned he confiscated his passport.

'But then Salman went to his mother and said he wanted to go on a pilgrimage to Saudi Arabia so she gave him back his passport and he came to England instead.’

Lina Ahmed, another member of south Manchester’s Libyan community, said Abedi’s grew increasingly erratic in the period leading up to the attack.

‘A couple of months ago, he was chanting the first kalma (Islamic prayer) really loudly in the street,’ she said.

‘He was chanting in Arabic. He was saying “There is only one God and the prophet Mohammed is his messenger”.

For a while, Abedi (circled) was a normal happy young kid who supported Manchester United, drank and smoked weed at parties. There is a no suggestion any of the friends he is pictured with have been involved in any wrongdoing

France’s interior minister Gerard Collomb revealed that both British and French intelligence services had information Abedi had been in Syria.

‘All of a sudden, he travelled to Libya,’ said Mr Collomb, ‘and then most likely to Syria, became radicalised and decided to commit this attack.’

Abedi’s sister Jomana suggested yesterday he wanted revenge for US air strikes in Syria.

It also emerged that his brother Hisham, who was photographed on social media brandishing an assault rifle, had been under investigation by Libyan authorities because they suspected links to ISIS.

He has now been arrested on suspicion of knowing all about the forthcoming attack and planning one of his own in Tripoli.

Two friends of Abedi allegedly became so worried they separately phoned the police counter-terrorism hotline five years ago and again last year.

‘They’d been worried he was “supporting terrorism” and had expressed the view that “being a suicide bomber was OK",’ a source told the BBC.

The bomber's father, Ramadan Albedi, published a picture of his son Hashem holding a machine gun while wearing a Nike t-shirt and combat trousers

A US official even briefed that members of Abedi’s own family had also contacted British police saying he was 'dangerous'.

This all prompts one simple question, doesn’t it - how the hell did Salman Abedi not get caught?

Today, much of the news coverage has been devoted to outrage over how and why US media have been able to publish highly confidential photographic material from the scene of the attack.

I agree it’s wrong and bloody annoying that US intelligence agencies have leaked this stuff from their British counterparts in this way.

But they’re acting purely from self-interest; they don’t want this happening in America. Every government is going to prioritise the safety of its own citizens right now.

What worries me far more than a few dumb leaks is the abject failure by our law enforcement and intelligence authorities to stop this utterly predictable mass murderer before he set off his bomb.

Salman Abedi was the perfect template for a radicalised Islamist terrorist, the exact type we had all been repeatedly warned about: a young, well-educated Muslim man drawn to the bright, brutal, barbaric lights of ISIS by anger and a twisted, deviant concept of what his religion stands for.

There are at least 3,000 others like Abedi in Britain right now; people whom our authorities have serious concern are radicalised jihadists.

Meanwhile, we have far fewer people to monitor them.

A US official briefed that members of Abedi’s own family had contacted British police saying he was 'dangerous'

British Prime Minister Theresa May was Home Secretary when police numbers were slashed by 20,000.

She was publicly warned, by a Manchester policeman who’d just quit in helpless disgust, that this draconian move would dramatically reduce the ability of police in the city to work out what was really happening in the community. He specifically said it would imperil police ability to protect the country from terror attacks.

Mrs May ignored that warning and is now reduced to sending soldiers onto the streets after that warning came back to haunt her.

Her government can boast, as it has been all week, about the many attacks Britain’s security forces have foiled.

But the hard reality is that ISIS-inspired terrorists have now committed two appalling outrages in Britain within a few weeks. Once on London’s Westminster Bridge, now in Manchester.

There will be more, of that we can all sadly be certain.

The big question is how to stop them?

First, hire many more police. Flood the damn streets with them, with orders to constantly poke their noses into every community where radicalisation has happened or is feared to be taking place.

Second, hire many more spooks. ISIS uses modern technology to communicate, so we need to get into that communication faster and more efficiently. That also means tech giants like Facebook, Google and Twitter doing far more to crack down on terrorists using their platforms to spread their evil message and instruct followers on how to commit terror.

Third, toughen the laws to make it easier to arrest, detain and if necessary deport those who are suspected of being ISIS sympathisers. They are far too weak at the moment, as any police officer will tell you.

Fourth, I repeat that the Muslim community is not doing nearly enough to identify and expose radicalized extremists hiding in their midst. Nor to prevent the disturbing growth in extreme Wahhabi-inspired teachings of the type ISIS encourages, in Islamic mosques and Muslim homes.

If the reports I mentioned earlier are true – and none has yet been officially confirmed by the authorities - then it would appear some members of the Muslim community DID do the right thing and reported Abedi for his suspicious behaviour.

I applaud this. It’s what HAS to happen.

But it’s not happening nearly enough.

Whether this is out of understandable fear of retribution, apathy or in a few cases, tacit support for what ISIS is fighting for, I don’t know.

But the situation has to change, not least because decent, law-abiding Muslims themselves are the biggest global victims of ISIS violence.

CCTV (left and right) taken in Manchester's Arndale Centre allegedly shows Salman Abedi shopping just three days before he blew himself up after an Ariana Grande concert. The thin man, wearing trainers and a baseball cap, was caught on camera on Friday night

The chairman of a second south Manchester mosque at the Salaam Community centre today revealed he also ejected Abedi just two months ago for staying over in the mosque.

‘I told him he had to leave,’ said Abdullah Muhsin Norris. ‘He said don’t treat me like a child. He is very easy to upset.’

He was then asked if enough was being done to tackle hugely dangerous extremist brainwashing of young Muslim men.

‘I don’t think you can ever do enough,’ he admitted. ‘Sometimes it goes in one ear and out the other. You have to keep trying.’

Norris added that he was changing his own personal reporting threshold in light of Abedi’s terror attack.

But it’s all too late for those poor young people slaughtered on Monday night.

This dreadful attack should and could have been stopped.

That is wasn’t, is a shameful dereliction of duty by every single person who had suspicions about Abedi but said nothing, who was given information and failed to act on it, or who inexplicably reduced our ability to investigate radicalism.

The blood of those poor young girls is on all their hands today.