It has been a long and controversial journey that began with Abid Naseer's radicalisation in Pakistan and ends in a maximum security prison in the US.
But although MI5 and police in Britain have been vindicated by the verdict in a Brooklyn federal court, this is a case which has raised a number of uncomfortable questions.
Why was Naseer not tried in the UK?
This would clearly have been the preferred route given that Naseer, a Pakistani citizen in the UK on a student visa, was accused of plotting to blow up people on the streets of a British city.
However, despite carrying out one of the largest ever counter-terrorism investigations - involving the surveillance of a dozen suspects, the Crown Prosecution Service said there was not enough evidence to put any of the men on trial.
There were emails between Naseer and a suspected al-Qaeda operative in Pakistan - allegedly coded discussions about a possible imminent attack on the city centre. But crucially no explosives or chemicals were found and no gathering of ingredients to make bombs.
The authorities felt they could not risk running the surveillance operation any longer.
Police were forced to move in more quickly than planned when secret operational details written on papers held by a senior detective were photographed as he was entering 10 Downing Street for a briefing.
A subsequent report by Lord Carlile, then the government's Independent Reviewer of Terrorism Legislation, found this would not have affected the issue of the evidence - but it criticised the lack of co-ordination between the police and the CPS during the investigation.
Why was Naseer extradited to the US?
This is one of a number of cases where critics suggest Britain is effectively sub-contracting difficult legal cases to the US - where juries are much more likely to convict terror suspects.
After the decision not to charge Naseer, the Home Office attempted to deport him to Pakistan, along with those other arrested men who had not voluntarily returned there. But the High Court blocked it because of the risk he would be mistreated.
At the same time they concluded Naseer was "an al-Qaeda operative who posed and still poses a serious threat to the national security of the United Kingdom".
So the UK authorities could not put him on trial, could not deport him and did not want him left free to roam the streets.
He spent a brief time on a control order but the dilemma was only resolved when US prosecutors announced they wanted to try Naseer in New York and he was extradited from the UK. They said - and the jury has now agreed - that he was part of a wider al-Qaeda conspiracy to attack Britain, America and Norway.
Lord Carlile told the BBC: "In every case you have to find where the most convenient forum is for the trial. That will depend on where the evidence lies.
"If the evidence lies in the United States, particularly the key evidence, then one would expect the trial to be in the United States."
What new evidence did US prosecutors have?
This has been a trial packed full of drama and interest. A string of MI5 officers wearing wigs and disguises were cross-examined by Naseer who was representing himself.
He also went toe-to-toe in court with a convicted al-Qaeda terrorist turned prosecution witness, but the two had never met.
The trial was the first to use declassified documents seized by US special forces in the raid on the Pakistan compound in which they found and killed Osama Bin Laden - the former head of al-Qaeda.
The court heard how an FBI agent waiting in a military hangar in Afghanistan for the return of their helicopter, saw Bin Laden's dead body before it was taken for burial at sea. The agent's job was to sift through the seized documents.
In a document titled Report on External Operations, one of Bin Laden's deputies told the al-Qaeda leader: "We had sent a number of brothers to Britainâ€¦ the brother determines what targets in line with what materials he can get." But none of the papers mentioned either Manchester or Abid Naseer.
Speaking exclusively to the BBC, Naseer's father, Nasrullah Jan Khattak, said: "It's easy to make accusations. They say my son is al-Qaeda but there was no proper evidence. The prosecution should have presented proof that my son was planning an attack."
Instead he claims there was testimony from surveillance officers who had observed Naseer moving around the north-west of England, saying he looked tense while on the phone.
"Whether he is happy or tense on the phone has nothing to do with al-Qaeda," said Naseer's father.
US prosecutors were not able to significantly strengthen the case against Naseer - but he was not able to adequately explain the coded email exchanges with the alleged al-Qaeda operative in Pakistan. The jury did not believe his account that this was innocent talk about trying to find a bride.
What would a British jury have made of this case? Well, that's a question to which we will never receive an answer.
Nearly six years after MI5 and armed police dramatically disrupted an al-Qaeda plot to launch suicide attacks on shoppers in Manchester, the ringleader has finally been convicted.