HEARTBROKEN families today slammed MI5 after a "significant missed opportunity" meant a terrorist was free to kill their children.
Salman Abedi murdered 22 people when he detonated a homemade bomb in Manchester in 2017.
A damning report today found MI5 were guilty of "a significant missed opportunity to take action that might have prevented" the atrocity.
The families of those killed in the blast have now told how they will never forgive the security services for letting them down.
Andrew Roussos' daughter Saffie-Rose was just eight when she was killed in the attack during an Ariana Grande gig.
He said: "Our beautiful little girl lost her life because of the failings of the security services and today's report acknowledges that MI5 might have prevented the bombing.
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"We all heard the evidence and knew there were failings, but hearing how this tragedy might have been avoided is devastating for us all.
"This was a cataclysmic failure, and it is clear from all of the evidence we have heard about Abedi that there were many opportunities for the security services to have ensured the bombing never happened.
"In my view the fact that MI5 failed to stop him despite all of the red flags available demonstrates they are not fit to keep us safe and therefore not fit for purpose."
Addressing the authorities on behalf of families of the victims, Caroline Curry, whose 19-year-old son Liam died, said: "Shame on you all.
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"We really hope lessons will be learnt this time."
Caroline also said they want the failures fixed so there won't be "as many families going through the utter heartbreak we have had to endure for the last five years, nine months, one week and one day".
She said the families hope "one day the whole truth will come out".
Ms Curry added: "Forgiveness will never be an option for such evil intentions and those that played any part in the murder of our children will never ever get forgiveness, from top to bottom, MI5 to the associates of the attacker," Ms Curry continued.
"We will spend the rest of our lives trying to protect our boys because as we found out through this process, once you leave your home you are on your own."
While Martyn Hett's mum Figen Murray said today is "not the day for looking back" but about "moving forward".
She added: "Terrorism continues to plague our society and as a nation we need to be better prepared to deal with it.
"It seems terrorists are always a step or two ahead of us and we need to catch up fast."
Terrorist Abedi had been on the radar of the security services for years before the bombing.
The report found the blunder by MI5 was partly down to a failure by a security service officer to act swiftly enough.
The "principal missed opportunity" was identified as two pieces of intelligence received by MI5 in the months prior to the attack.
These were not disclosed in the report or shared by spooks with counter-terror police in the North West.
The intelligence was assessed to relate to "non-nefarious activity or to non-terrorist criminal activity".
Had further steps been taken, Sir John said it would have "increased the overall prospect that the attack would have been prevented".
He added: "We cannot know what would have happened, but there is at least the material possibility that opportunities to intervene were missed."
The grieving father spoke out ahead of the third and final report on the bombing, which was released this afternoon.
It found MI5 were guilty of "a significant missed opportunity to take action that might have prevented" the bombing.
The document also described Abedi as like "a Petri dish brimming with germs" after his parents fled to Libya in 2016.
This meant his radicalisation was driven by "noxious absences and malign presences" that allowed him to spiral further into Islamist extremism.
The report also found Abedi should have been put on the anti-terror Prevent programme in 2015 and 2016.
The homegrown terrorist was also flagged to MI5 on other occasions amid fears he was mixing with terror suspects.
A meeting to consider further investigation of the warped jihadi was scheduled for 31 May 2017- nine days after the bombing.
Abedi was instead able to carry out the deadliest terror attack in Britain since 7/7 undetected.
Saffie-Rose's dad earlier slammed the secret service and said he wants bosses to fess up to the fact they made mistakes, and let Abedi "slip through the cracks".
He told : "Salman Abedi should have been stopped before he got to that arena and that's MI5's job.
"They know the threat, they know what these people do and don't do, they know where to look and not to look, and they were more prepared than what Manchester was that night - so MI5, for me, have got blood on their hands."
Andrew added: "I want them to admit that with all the signs and what they knew about this family and Salman Abedi that they let it slip through the cracks, because they did."
For months the Manchester Arena bombing inquiry has heard from the secret service behind closed doors.
Today's report outlined the role spooks played in the months and years leading up to the attack.
It also looked into the bomber's links to the convicted terrorists, and the radicalisation of the Abedi family.
Chairman of the inquiry Sir John Saunders said: "It is not possible to reach any conclusion on the balance of probabilities or to any other evidential standard as to whether the attack would have been prevented.
"However, there was a realistic possibility that actionable intelligence could have been obtained which might have led to actions preventing the attack."
In November last year, a critical report found at least one of the victims would have survived the attack had it not been for the "inadequate" emergency response.
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Following the findings, Saffie-Rose's family made the heartbreaking statement that victims were failed by emergency services on an "unfathomable scale".