Our US correspondent Mark Stone takes stock of a remarkable and fast-moving day in the investigation over leaked US military documents – some of which concerned the Ukraine war.

A remarkable leak, a breathtaking breach of security, a strain on America’s alliances globally, and on Thursday afternoon it all came to a dramatic end in a rural corner of Massachusetts.  

The day’s events were very fast moving and began not, as might have been expected, with breakthroughs by the authorities investigating the leak, but instead from a series of remarkable investigations by the media. 

First, a scoop from the Washington Post newspaper which revealed that an individual had leaked the information to a small circle of online friends on a social media platform called Discord, popular with gamers. 

The Post obtained an interview with a member of the group who claimed the documents had then been disseminated out beyond the closed group.

By late morning, The New York Times, working with the open-source investigators Bellingcat, published a trail of digital evidence which they claimed identified Jack Teixeira, a 21-year-old Air National Guardsman, as the leader of the Discord group where the documents first appeared. 

Journalists were on the doorstep of his family home in rural Massachusetts while the Pentagon spokesman struggled to tread water from a flood of questions about the morning’s revelations. 

But as Brigadier-General Pat Ryder spoke, an arrest came. 

The cable news networks already had their helicopters over the Massachusetts countryside and beamed live images of the heavily-armed FBI agents arriving and then arresting Jack Teixeira. 

The US attorney general, Merrick Garland, then made a statement confirming the news that viewers had just watched. 

It appears American authorities have been on the backfoot at every turn with this case. They now claim to have their leaker. He will go through the judicial process. They will be relieved, at least, that he appears not to be a foreign agent. 

But they have many questions to answer: how did a 21-year old Air National Guardsman have access to these documents? Was he entitled to the access? Are there more classified documents out there? Why did it take so long, with media help, to find him?

More broadly, America’s allies need to be reassured that their secrets are safe in American hands. Trust needs to be rebuilt beyond the damage they know has already been done.