There is no “definitive” answer as to why Salman Abedi became a mass-murdering suicide bomber but his radicalisation was driven by “noxious absences and malign presences”, the final report into the Manchester Arena attack concluded.

The 207-page report by chairman Sir John Saunders cited Abedi’s disengagement from mainstream English education and the absence of his parents who left their Manchester home for their native Libya in 2016, leaving no parental supervision or presence.

Abedi’s descent into violent Islamist extremism was also prompted by the ongoing civil war in Libya and Abedi’s “radicalising” friends and family.

The third and final report following the Manchester Arena Public Inquiry, which was published on Thursday, dealt with the issues of “preventability” of the attack on May 22 2017, in which Abedi murdered 22 people.

It also dealt with how Salman Abedi, and his brother Hashem, became radicalised – laying the blame mostly on their own family. His father Ramadan Abedi and mother Samia Tabbal, who came to the UK from Libya seeking asylum, are both cited in the report.

None of Salman Abedi’s family, his parents or older brother Ismail co-operated with the public inquiry.

Abedi had been a weed-smoking, university drop-out, with a “lazy” and disruptive attitude to education, before he began to change his behaviour and appearance and became more religious and judgmental, the public inquiry heard.

Abedi, 22 at the time of the bombing and Hashem, two years his junior, who was jailed for life for his part in the plot, had both travelled from their home in south Manchester with their father to Libya in 2011 during the civil war there, and likely were involved in the fighting.

Ramadan Abedi had made clear his support for suicide attacks in the Libya conflict on Facebook.

Both brothers were rescued by the Royal Navy from Libya in 2014.

The report says both Abedi brothers were radicalised in Libya, where it is “probable” they got training or help in how to build a bomb.

“Ramadan Abedi instilled in his sons, extremist views and encouraged them to put those views into practice when he exposed them to training with and combat alongside Islamist militias…,” the report said.

After their parents left the UK for good around 2016, there was a “notable change” in the brothers’ behaviour, and they suddenly became “very devout, very religious”.

By then, both had become “thoroughly radicalised”, the report stated.

Sir John’s report said it is “possible” that had either been referred to the Government’s anti-terror scheme, Prevent, there may have been some “positive benefit”.

Hashem Abedi later confessed the attack was done in support of terror-group Islamic State.

The report said the group’s rise from around 2014 is likely to have provided the “trigger for a shift in worldview which could envisage an attack in Manchester”.

But while their family hold “significant responsibility” for the brothers’ radicalisation, there is “insufficient evidence” any of them had specific knowledge an attack was being planned, the report states.

Outside their family, the Abedi brothers were also subject to malign influences, the report concluded.

Some of Salman’s friends were involved in drug-dealing and crime, leaving him with “almost no close connections or friendships that would tie him to law-abiding society,” the report said.

One good friend of the brothers, Abdalraouf Abdallah, had a “hero” status with local youngsters – though he was later convicted of terrorism.

The area of south Manchester where the brothers lived was also identified as a problem area by the Joint Terrorism Analysis Centre, with issues of radicalisation and crime.

Concluding with the evidence given by terrorism expert Dr Matthew Wilkinson, the report said: “I have never seen such a complete picture of the Petri dish absolutely brimming with germs.”