US President Barack Obama last week chose to veto legislation that had been passed by both US Congress and the Senate. Citing the national interest, Obama vetoed laws that would allow the families of 9/11 victims to sue the Saudi Arabian government for their loss. On Wednesday the US Senate fought back, voting 97-1 against the veto, followed by Congress similarly voting 348-77. Ordinarily, this would mean the proposal would become law. But it’s unlikely to be over yet.

Use of Presidential veto isn’t as rare as an Australian Governor-General withholding Royal Assent: Obama has exercised veto no fewer than 11 times, including four times this year.

But the ‘Justice Against Sponsors of Terrorism Act’ (JASTA) has attracted attention like no other. That’s because it arose from the deadliest terrorist attack in US history, with mysterious possible links to Saudi Arabia. And a Presidential veto is rarely rebuffed.

Obama’s vetoing of the legislation provides insight into the challenges of unravelling terrorist support networks, as well as the ways in which domestic concerns can sometimes uncomfortably clash with international norms. It also brings to the fore once again the vexed issue of intelligence versus evidence.

The story starts with the US Joint House Inquiry into intelligence in connection with the 9/11 attacks. Conducted prior to the larger and better-known 9/11 Commission, it reported in 2002—less 28 redacted pages.

The ‘28 pages’ were reported to contain information on foreign state sponsor support for Al Qaeda, including possible Saudi connections with the terrorists. The Saudi reference caused much comment in the intervening 14 years, ranging from inquiry members seeking to declassify the pages, activists suggesting that the report implicated official Saudi support for the attack, and even the Saudi government requesting the pages be released to stop the harm to Saudi reputation.

Meanwhile, a group representing families of 9/11 victims succeeded in getting support for legislation to relax sovereign immunity in cases of terrorism to allow the Saudi government to be sued for any role in the attacks.

The JASTA bill proceeded through Congress and was ratified by the Senate in May this year. The ‘28 pages’ document was released in July 2016. President Obama vetoed the legislation on 23 September; conspiracy theorists might note this was also Saudi National Day.

But what do the ‘28 pages’ actually say about Saudi involvement? And does it make sense for Obama to veto the legislation?

The ’28 pages’ provide a range of information on possible Saudi links to 9/11 plotters, including allegations that support was provided to some of the 9/11 hijackers by people who may’ve been connected to the Saudi Embassy in the US. The possible support included the then Saudi ambassador giving money to a person known to have supported two of the hijackers, and a consular official in Los Angeles assisting two more. Other information includes phone numbers connected to individuals associated with the Saudi embassy found in the possession of an Al Qaeda associate.

From an intelligence perspective, such information has value in identifying leads for possible further collection and analysis. Augmented by more information, this might contribute to an intelligence assessment. That is, a subjective and weighted judgement, not a watertight statement of fact.

From an evidentiary point of view the information provides little of substance. The 2002 Joint Inquiry report (PDF) observed that it wasn’t its task to ‘conduct the kind of extensive investigation that would be required to determine the true significance of any such alleged support to the hijackers’.

The subsequent 9/11 Commission—which did have this investigatory function—examined many of the leads and concluded that it found no evidence that the ‘Saudi Government as an institution, or senior Saudi officials individually funded Al Qaeda’. A 9/11 Review Commission reported in 2014 there was no new evidence that would change the Commission’s findings on responsibility for the attacks.

On releasing the declassified pages in July, White House Press Secretary Josh Earnest affirmed this view, stating the document didn’t change the US government’s previous assessment on possible Saudi involvement in 9/11.

Intelligence leads are one thing and hard evidence another. And it’s evidence that would be required for a civil suit. Allegations mightn’t be credible nor able to be proven (although the standard of proof required in a US civil suit is lower than a criminal case). Association or general support for individuals or organisations doesn’t necessarily imply knowledge that a terrorist act would be committed. And the actions of individuals mightn’t reflect official views, as seen with the recent case of World Vision’s Gaza manager providing funds and other support to Hamas.

So, despite speculation over the past 14 years, the ‘28 pages’ isn’t a smoking gun on Saudi involvement in 9/11. But it has opened a Pandora’s box for US sovereign immunity.

A lesson for governments from this saga is that withholding information on matters of high public interest may have unforeseen and inadvertent consequences. Doubtless the CIA and FBI elected to redact this information for good reason—protecting sources and the privacy of those named. But that created angst not only in the electorate but also among the elected. For the Senate to unanimously support JASTA speaks to a breakdown of understanding and trust between government institutions and politicians.

President Obama was correct to veto the legislation. International law provides immunity of sovereign states to the domestic laws of other countries. To allow US citizens to sue the Saudi government would challenge this norm and ultimately damage the US.  If the ’28 pages’ did, however, demonstrate Saudi culpability, the matter should be pursued through the international—rather than the US—legal system. In his advice to the Senate, Obama cited damage to US international interests across the gamut of military, diplomatic and business affairs, as the law could lead to counter-suits against US activities overseas.

For now the issue will continue through the US political process. Despite the strength of support from legislators for JASTA, it’s hard to see how such a challenge to international norms could ultimately succeed. But Australia and the US need to be prepared if it does.