Flowers and Jubair’s trial heard they were part of the cyber-crime collective, Scattered Spider.
The loosely organised gang of young English-speaking cyber-criminals has been linked to dozens of other cyber-attacks including on retailers Marks and Spencer and the Co-op.
But the BBC has learned Flowers initially came to the attention of police shortly after he turned 16 years old.
In October 2023 he was caught carrying out low-level cyber-crime and visited by West Midland’s Regional Cyber Crime Unit prevent officers.
Police say that during the visit Flowers did not engage with officers and was given a cease and desist order to deter him from further offending.
Police had the option to invite him to enrol in the national Cyber Choices programme, which works to steer young people away from cyber-crime.
However Flowers was already being investigated for an offence and was reluctant to engage with officers, so they deemed him not suitable.
Just months later, the teenager – who was living with his grandmother – went on to commit a series of increasingly serious cyber-offences with Scattered Spider which culminated in the TfL attack.
NCA deputy director Paul Foster, head of its National Cyber Crime Unit, said the case highlighted the challenges posed by a small number of highly capable offenders.
He called for stronger legal powers – such as the proposed Cyber Crime Risk Orders (CCROs) – to deal with cases like this.
CCROs, announced by the UK government as part of planned reforms to the Computer Misuse Act, are designed to let police and courts place restrictions on people considered high risk before they carry out further serious breaches.
They would “enable earlier law enforcement interventions against high-risk cyber-crime offenders,” Foster said.