The lawyers provided The New York Times with excerpts of the material they had amassed by putting together the pieces from leaking American intelligence documents among other things, the daily reported on Tuesday.
The evidence, originally presented in hundreds of thousands of pages, recount how the Saudi royalty would use middlemen and financial supply routes to bankroll militants based in Afghanistan and Bosnia.
Prince Turki al-Faisal is alleged in the evidence to have delivered up to a one-billion-riyal (USD 267 million) check to a top Taliban leader through an envoy in 1998.
Prince Salman bin Abdul Aziz and other royals were also accused in a German intelligence report of using a Saudi charity as a stopover for the funds. The report named Pakistan as yet another destination for the assistance.
The family, which had strong ties with the Bush administration, is also suspected of having reinforced the militancy otherwise and enlisted militant agents using intermediaries including the Saudi High Commission for Aid to Bosnia.
Based on the claim, a royal family can evade legal and criminal action citing "potentially significant foreign relations consequences." In some cases, governments have waived this immunity to allow for suits.
The Justice department though is said to have destroyed the critically compromising documents, which had leaked to the lawyers.
Fifteen out of the 19 hijackers of the commercial planes that crashed into the Twin Towers of the World Trade Center and the Pentagon are reportedly Saudis - and none were from Iraq.
The royals say the case misuses the common nationality and is built on, what they call classic accusations of the type.
The five detainees held in US custody for related charges have accepted responsibility for the attacks.
The lawyers for the family have also spared no effort in stemming the move. "In looking at all the evidence the families brought together, I have not seen one iota of evidence that Saudi Arabia had anything to do with the 9/11 attacks," said Michael Kellogg, a Washington lawyer representing Prince Muhammad al-Faisal al-Saud in the lawsuit.