On a Sunday afternoon the week before Christmas, journalist Laura Halminen smashed her laptop with a hammer, causing it to spark and smoke. Her actions set off a chain of events that lead to one of the biggest debates about security and press freedom in Finnish history.

A day before she attacked her computer, Halminen had co-authored a big investigative piece in Finland’s largest and oldest newspaper, Helsingin Sanomat. The story was based on highly classified documents about the Finnish Intelligence Research Center — a branch of the military so secret that before this article came out, the Finnish public did not even know what exactly the center really did. According to the article, the center uses signals intelligence to spy on the Russian military.

For years, Finnish journalists had fought in court to get some documents about the center released — and they lost. But Halminen got the documents from a whistleblower, and to protect her source, she took the extreme measure of hammering her laptop into a smoldering mess.

When Halminen called for help putting out the fire, not only did fire trucks arrive at her Helsinki apartment; so did the police and later, the KRP, which is like Finland’s FBI. They suspected Halminen was destroying evidence, so they searched her home, seized her broken laptop, her phone and USB sticks — all without a warrant from a judge.

Almost as soon as the article was published, some Helsingin Sanomat readers called in or wrote letters rebuking the paper for giving away military secrets and potentially antagonizing Russia, Finland’s adversarial neighbor to the east. High-ranking government officials, including the defense minister, accused the newspaper of being unpatriotic and harming national security. President Sauli Niinisto called for a criminal investigation into the newspaper.

“There’s been an overreaction to the publication of these articles,” said Martin Scheinin, a Finnish professor of international law at the European University Institute. Scheinin, who spent years at as a UN special rapporteur working to protect human rights in the course of counter-terrorism efforts, sees the government’s response to the article as an attack on freedom of the press.

The criminal investigation into the newspaper has been going on for more than six weeks and could lead to serious criminal charges. According to Paivi Korpisaari, a professor of communications law at Helsinki University, the journalists could be charged with the crime of disclosure of a national secret. This law is part of a rarely-used section of the criminal code relating to treason.

Korpisaari doubts the journalists would have ever imagined the possibility of such charges. “Usually journalists think that the one who is leaking the information illegally is the only one who is responsible.” In fact, the law prohibits not just the leaking of classified material, but also its publication.

Still, Korpisaari says this law is an obscure one, “I don't remember any case where somebody would have been charged of this crime.” In fact, she says, this is the first time that classified documents relating to national security have been leaked to and published by the Finnish press.

In Finland, charging journalists with treason would be an extraordinary measure. The country currently ranks third in the world for press freedom, and it has had laws about government transparency for more than 200 years.

So, what did Helsingin Sanomat publish that could pose such a grave threat to national security? The part of the article that is most criticized is the pictures, which show actual classified documents with stamps marking them “top secret.”

But Scheinin doesn’t think they’re a problem. The pictures show only small parts of the documents, all of which are more than a decade old, and he says, “there was no technical information published that would reveal any secrets about the actual methods of surveillance.”

Furthermore, those technical details were already public knowledge, published six months earlier in a newspaper more supportive of the current governing coalition in Finland, said Scheinin. “I find it strange how this now could be a threat to national security when the same things were reported in a different light earlier by another newspaper.”

But some Finnish national security experts say the threat is real. “If [the Finnish military] classified something, then there is a reason for that,” said Hanna Smith, the academic director at the Helsinki-based European Center of Excellence for Countering Hybrid Threats. Hybrid threats include not only military and political threats, but also informational threats, like Twitter bots and fake news.

Smith, whose research focuses on Russia, says that one reason the document leak is problematic is that most of it deals with spying on Russia. Finnish history is pockmarked by Russian aggression: multiple wars and a hundred years of Russian imperial rule. Even after Finland finally gained its independence in 1917, the Russian threat never really went away.

“It's not that Finland is afraid of Russia,” said Smith, but Finland knows that it “needs to be wary that Russia has an interest beyond its own borders.”

As a small country of just 5.5 million people, Finland can’t afford to antagonize Russia. That’s why, for instance, Finland hasn’t joined NATO, the military alliance between the US and much of western Europe. According to Smith, “Russia took the stand of actually threatening Finland: Bad things will happen to Finland if it will join NATO.”

To get the point across, Russia sometimes sends military jets into Finnish airspace. Smith says if Russia were to attack, Finland doesn’t expect anyone to swoop in to the rescue. “The whole Finnish security thinking today is that we need to somehow take care of ourselves and as long as possible to be able to hold out” in case of a Russian attack.

Making Russia think twice about attacking means Finland needs to maintain a defensive edge: rigorous and secret intelligence programs. Putting classified information about the Finnish Intelligence Research Center out in the open could erode that defensive edge.

Ilkka Kanerva, the chairman of the defense council in the Finnish Parliament, would agree. In an interview with the TV network YLE, Kanerva said, “In addition to the obvious risks” — meaning, Russian intelligence — “this document leak indicates that Finland can’t be trusted to keep secrets. This has caused difficulties with Finland’s national security partners.”

The leaked documents about Finland spying on Russia are a real cause for concern. But Smith, like Scheinin, concedes that the information the newspaper printed doesn’t seem that sensitive. What’s worrying is the leak itself and how this type of material made its way to a journalist.

How can we know that the leaker wasn’t compromised? That he or she wasn’t influenced by Russia?

The editor in chief of Helsingin Sanomat, Kaius Niemi, gave a TV interview two days after publishing the article. When the interviewer asked how he could be sure the article wouldn’t harm national security, Niemi said, “We vetted our sources, made sure there wasn’t anyone behind the source trying to influence the story, and we understood all the risks.”

If the real national security threat isn’t the information the paper printed, but rather the leak itself, why did the authorities focus on the journalists more than the leaker? And where did the leak even come from?

Martin Scheinin has a theory: “the possibility that the leak comes from the president's office has triggered a strong reaction as a kind of defense mechanism — and then you blame the journalists. But I find it highly likely that the authorities already know who the leaker really is, even if that is not discussed in the public.”

Scheinin thinks the journalists are being punished for throwing a wrench into a new bill that would allow for the mass surveillance of Finnish citizens. The Helsingin Sanomat article revealed the scope of the surveillance program and the extreme level of secrecy around it. In doing so, it showed that the type of surveillance Finnish lawmakers want to legalize may already have been going on for years.

“The legislation in the making is quite sensitive and problematic,” said Scheinin, “authorities may feel a degree of panic that there they are getting a bad reputation.”

But, he said, the fact that the government wants to build a legal framework around these surveillance programs is a good thing. The problem is that “this is done completely secretly without transparency” and these policies were never open to public debate.

It could take months to conclude the investigation into whether the journalists committed treason. But whether or not they’re convicted, Scheinin says, this has already had a chilling effect on press freedom. The original article promised a whole series of stories about the leaked documents. But since the investigation began, the newspaper hasn’t released anything significant.

“People think that Finland is a model country for freedom of expression,” said Scheinin, “but actually respect for freedom of expression has not been internalized.”

At the very least, concerns about press freedom and government transparency aren’t taking precedence over fears about Russia. An overwhelming majority of Finns just voted to reelect President Sauli Niinisto, a conservative known for being extremely cautious with Russia. This public support could make it easier to pass the surveillance bill, which will soon come up for a vote.

A month after the newspaper article came out, the coalition government decided to expedite the vote on the surveillance bill, saying that national security concerns had recently become more urgent.

Mari Karppinen contributed reporting to this story. A previous version of this story misspelled Martin Scheinin's name.