Questions for police over terror plotters' network
Two men have been convicted of planning a drive-by terrorist attack in London. The investigation into the plot led police and MI5 to uncover a trail of radicalisation involving British students at a university in Sudan.
But did the UK authorities miss a vital opportunity to stop more young Britons from being recruited by IS?
The trail started with British students Tarik Hassane and Suhaib Majeed.
Police kicked down the door to Hassane's west London home in the early hours of 7 October, 2014, as they attempted to avert a terrorist attack on the capital.
It was when they examined Majeed's phones that they discovered the pair had been part of encrypted discussions on social media, including as part of a group calling itself the Turnup Terror Squad.
It was here, they found, that medical student Hassane had pledged allegiance to the so-called Islamic State group.
Police and MI5 also found vital intelligence on others in the group - many of them fellow-students of Hassane from the University of Medical Sciences and Technology (UMST) in Sudan, where he had gone to study after doing badly in his A-levels.
His fellow students were the children of middle-class professionals, many of whom had sought asylum in Britain years earlier.
Those parents had sent their sons to study in Sudan to reconnect with their roots and, in some cases, in the misplaced hope of removing them from extremist influences in the UK.
In the months following Hassane's arrest, at least five of his friends were able to leave for Syria - despite having featured in the police investigation and being known to the UK authorities.
Al-Qaeda or IS?
Members of the Turnup Terror Squad included Ayman Aziz from London, Mohamed and Ibrahim Ageed, the sons of a doctor from Leicester, and Mohammed El-Raba'a from Kettering.
Aziz had known Hassane, now 22, and physics student Majeed, now 21, since nursery school.
He was especially close to Majeed, with chat logs showing the pair argued late into the night about whether to support al-Qaeda or IS.
Aziz was a hard-line supporter of IS and, like Hassane, had adopted extreme views before leaving London for Khartoum.
Aziz was photographed with Majeed as part of the surveillance operation that police and MI5 launched in the summer of 2014.
It was Aziz who had persuaded Hassane to join him at UMST, where he started his course in September 2013.
Once there, the two friends from Ladbroke Grove met other British students, also alienated from the values of their home country.
The group coalesced around a British-Palestinian graduate, Mohamed Fakhri Al-Khabass, whom the BBC has previously exposed as having played a key role in radicalising students at UMST.
Documents seen by the BBC suggest he had been targeting British students to indoctrinate. He was able to continue to do this even after appearing on the edges of the police investigation into Hassane.
The Turnup Terror Squad also made frequent reference to "Shaykh Saddiq," a cleric in Khartoum to whom they looked for guidance.
The BBC understands this is Shaykh al-Sadiq Abdallah Abd-el-Rahman, a cleric who was arrested by counter-terrorism police in Saudi Arabia in 2004 and deported to his native Sudan.
'Alert the families'
Dr Ahmed Babikir, dean of UMST, told the BBC that college authorities were not informed of any concerns about their British students, adding that "receiving information on time after the Tarik (Hassane) investigation might have enabled us to alert the families".
The BBC has also spoken the family of one UMST student who featured in the investigation. The family did not want to be identified but said they would have tried to stop the young man abandoning his degree to join militants had they been alerted by police.
This student, along four others, left the Sudanese capital Khartoum in June 2015 to join IS.
Ten other British students from the college, including Al-Khabass, had gone before them - leaving for Syria in March 2015.
Neither the police nor MI5 would comment on suggestions that they should have contacted either the families or UMST with their concerns.
During their initial investigation into Hassane, their focus would have been on rounding up those who posed an imminent threat to the British public.
The question of what they should have done afterwards is complicated by the fact the students were studying in a foreign country with a dubious human rights record and which critics say turns a blind eye to Islamism.
Because of this it may have been difficult for British intelligence agencies to share what they knew with their Sudanese counterparts.
And so it appears recruiters and radicalisers had easy access to the British students - though members of the Turnup Terror Squad already held some extreme views.
'Scars and trauma'
Parents of the UMST students did not understand how vulnerable their children were to the rhetoric of the radicalisers and recruiters or how Sudan had seen an influx of radical preachers, eager to use the conflict in Syria to spread their jihadist ideals.
Rashid El Sheikh is a Sudanese parent living in London who has seen two of his sons leave to fight with IS.
The youngest, Mamoud, was killed last year after getting to Syria from Sudan.
Mr El Sheikh says many of the British-Sudanese students, as the children of refugees, came "from a chaotic situation with some scars and trauma in the family… There are cracks in their psyche".
He believes the extremists fed into those feelings of insecurity.
Meanwhile Suhaib Majeed - who was thinking of doing a master's degree - and Tarik Hassane - who once dreamed of being a heart surgeon - are now facing decades behind bars.