And now this. A source close to the investigation says an Iranian-linked motive looks most likely. A Russian sabotage operation and an Islamist plot are also being checked.
Police have put a 400-metre cordon around the base. 85 homes in the village of Whelford have been evacuated. All five men are still in custody. Nobody has been charged.
That's everything we know.
Why this mattersRAF Fairford is not just any air base.
B-1 bombers have flown from there to hit Iranian missile sites — the ones attacking ships in the Strait of Hormuz. Britain gave America permission to use Fairford for exactly that, earlier this year.
And that permission made Fairford a target. In Iran's own words.
A couple of months ago, Iran's Revolutionary Guards warned Britain straight out: any base used to launch attacks on Iran becomes a legitimate target for Iranian forces. They named the B-1 bombers at Fairford specifically.
So when investigators say Iran looks like the most likely link here, they're pointing at a threat Iran already made in public. Two months before three vans turned up heading for that same base.
Wes Streeting, Britain's Defence Secretary, wouldn't talk about the specifics of this case. But he said Britain regularly has to stop Iran and its proxies trying to do harm. Shabana Mahmood, the Interior Minister, has separately accused both Iran and Russia of using proxies to run criminal activity inside the UK.
And this isn't a one-off warning sign. British military sites have been targeted by drones more than 300 times in the past year, according to recent reports. A few months ago, Britain sanctioned 12 people and groups linked to Iran, accusing them of plotting attacks and funding destabilisation inside the country.
The US Air Force's 501st Combat Support Wing, based at Fairford, says none of its troops were involved and that it's in close contact with UK police. Andy Burnham, the Prime Minister, has been getting regular updates and cancelled at least two events at his party's conference over this.
Iran's position hasn't moved. It has repeatedly denied being involved in attacks or plots in Britain or anywhere else, and it hasn't commented directly on this investigation.
Here's what nobody has said yet. Who the five men are. What nationality they hold. Whether they were working for a state or acting alone. And what, if anything, was actually found inside those vans.
Until that comes out, the strongest thing said out loud by anyone in authority is Donald Trump's own words for the intent — big damage — aimed at a base Iran had already named as a target.
