Glenn Greenwald's partner, David Miranda, was carrying a stunning amount of government documents when he was detained by British authorities for nine hours earlier this month.

And a U.K. national security adviser said Friday that some of those 58,000 documents were extremely sensitive to national security.

The Daily Telegraph's David Barrett tweeted out some of the details from the statement made Friday by Oliver Robbins, deputy national security adviser for intelligence, before U.K. judges.

Robbins was making the case that national security teams and police needed to investigate the material, which they seized earlier this month. The court extended an order Friday that will allow officials to continue to inspect the material seized for national security purposes.

Some of the key points of the statement, which intelligence analyst Joshua Foust called "extraordinary":

Robbins said that the case material included 58,000 documents that were " highly classified UK intelligence documents."

Among the documents was a piece of paper with the decryption password.

Police decrypted one file on Miranda's hard drive with the password.

The material contains " personal information that would allow British intelligence staff to be identified," including overseas.

Because of the size and scope of the material gathered, the British government believes that Edward Snowden " indiscriminately appropriated material in bulk."

In what could be a particularly troubling development, the UK government has "had" to assume that Snowden's data is in the hands of foreign governments to which he has traveled: Hong Kong and Russia. (Greenwald told Business Insider last week that it was "highly unlikely" that had happened, however.)

Robbins argued that it is "impossible" for Greenwald or any other journalist to determine which information could damage national security.

"The material seized is highly likely to describe techniques which have been crucial in life-saving counter-terrorist operations, and other intelligence activities vital to U.K. national security," Robbins said.

"The compromise of these methods would do serious damage to U.K. national security and ultimately risk lives."

The government told The Guardian newspaper that it had "no confidence in their ability to keep the material safe," and that the government "appeared to accept our assessment that their continued possession of the information was untenable."

Miranda, 28, was detained for nine hours at London's Heathrow Airport earlier this month under a U.K. anti-terror law, while traveling home to Brazil. He had spent a week in Berlin visiting journalist Laura Poitras, who has been working with Greenwald to publish stories based on leaked information from former NSA contractor Edward Snowden.

Miranda is taking legal action against the government. He has argued that his detention was a misuse of Schedule 7 of the U.K. anti-terror law and breached his human rights.

Miranda's trip, which was paid for by The Guardian, had the purpose of him being a courier between Greenwald and Poitras. Using encrypted thumb drives, he delivered documents to Poitras, and he came back with documents meant for Greenwald.

In a statement after Friday's court hearing, Guardian editor-in-chief Alan Rusbridger said that Robbins had made a "number of unsubstantiated and inaccurate claims" in his statement:

"This five-week period in which nothing has happened tells a different story from the alarmist claims made by the government in their witness statement," Rusbridger said.

"The Guardian took every decision on what to publish very slowly and very carefully and when we met with government officials in July they acknowledged that we had displayed a responsible attitude. The government's behaviour does not match their rhetoric in trying to justify and exploit this dismaying blurring of terrorism and journalism."

Greenwald blasted Miranda's detention at the time, comparing it to mafia-style methods:

This is obviously a rather profound escalation of their attacks on the news-gathering process and journalism. It's bad enough to prosecute and imprison sources. It's worse still to imprison journalists who report the truth. But to start detaining the family members and loved ones of journalists is simply despotic. Even the Mafia had ethical rules against targeting the family members of people they felt threatened by. But the UK puppets and their owners in the US national security state obviously are unconstrained by even those minimal scruples.