In a HARDtalk interview on 24 March, Roger Bolton talked to the leading expert in Al Qaeda's finances,
It was Jean-Charles Brisard who first made public the connection between Jamal Zougam, currently being held for the Madrid bombings, and one of the 9/11 conspirators.
He says also there's clear evidence linking him to the former head of the Madrid Al Qaeda cell and to Mohammed Fazazi, jailed for 30 years for last year's bombings in Casablanca.
Yet the Spanish police dropped surveillance on Zougam, even though both French and Moroccan intelligence services were interested in him.
Jean-Charles Brisard says governments do not share information on a permanent, daily basis, and they should.
Brisard is the chief investigator for the lawsuit representing 6,000 families of 9/11 victims against those who support Al Qaeda financially.
He has set up a huge database with information collected from intelligence sources in 35 countries, and plans to make it available to governments.
Jean-Charles Brisard told Roger Bolton that the attacks on 9/11 cost $500,000, and Al Qaeda's annual budget was around $50 million a year.
He said ninety percent of the money trails lead back to Saudi Arabia.
Brisard also warned that extremist operatives supporting Al Qaeda were active in Bosnia.
"Al Qaeda is fighting against democracy all over the world, and it will be a very long war".
HARDtalk can be seen on BBC World at 04:30 GMT, 11:30 GMT, 15:30 GMT, 19:30 GMT and 00:30 GMT
It can also be seen on BBC News 24 at 04:30 and 23:30