- Shahan Choudhury was accused of taking part in a murder when he was 18
- He was acquitted in 2007 but radicalised while on remand in Belmarsh Prison
- His family followed him to Syria last year - paying for it with 'housing benefits'
- A former prisoner warns Belmarsh has become 'like a jihadi training camp'
Shahan Choudhury, 30, vanished from his flat in London last year and has since used Twitter to urge other British Muslims to carry out terror attacks in the UK.
His family say he was 'brainwashed' after spending 18 months on remand in HMP Belmarsh for allegedly taking part in the stabbing of a 17-year-old.
He has been joined in Syria by his wife and three children, including a baby.Shahan Choudhury allegedly took part in stabbing a 17-year-old to death over a £15 debt when he just was 18
According to the Sunday Times the family's escape may have been funded by housing benefit payments.
Choudhury's wife Mehak is alleged to have traveled to Syria in early 2016, a few months after her husband.
The family's landlady discovered that Mehak had received a monthly housing benefit payment of £1,000 - which she'd failed to pass on as rent.
Shahan Choudhury first came to the police's attention when he was charged with being part of a gang who stabbed a 17-year-old hospital worker to death over an alleged £15 drug debt.
Hate preacher Anjem Choudary has been blamed for more than a dozen brainwashed radicals joining ISIS from the UK
He was acquitted in 2007 but his family believe he was 'brainwashed' by Islamic extremists at HMP Belmarsh.
As soon as he was released he joined the banned al-Muhajiroun (ALM), the hate group led by Anjem Choudary which has called for the implementation of Sharia Law in the U.K.
A relative said: 'He was just like any other western kid when he went in but by the time he came out he was going on about religion and how the kuffar [non-believers] would all end up in hellfire.'
Mehak was also radicalised halfway through her A-levels, according to her family.
Her father, Mohammed, said: 'I told police at the time that my daughter was becoming brainwashed and was involved with these people.
'But they told me there was no evidence of extremism and that, as an adult, she could do what she wanted.'
HMP Belmarsh has become 'like a jihadi training camp' according to one former inmate.
He told the Evening Standard: 'The problem is that Belmarsh is also a holding prison and so young people are brainwashed and indoctrinated and then go out into the wider prison system and create wider Akhi networks.
'Governors, prison officers and imans all know about this.'
More than a dozen disciples of Anjem Choudary have managed to join ISIS - despite some of them being on the security service's radar.
Three other of Choudary's followers will challenge the anti-terrorism controls they have been placed under later this week at the High Court .