In April 2019, a CIA officer on a work trip to London was jolted awake in his hotel room shortly after 1am by the most intense head pain he had ever experienced, sweating and losing his sense of balance. At his meeting the next day, he found he could not remember the names of colleagues he knew well and could barely follow the discussion.

A CIA officer struck in London and Warsaw

Five months later, asleep in a Warsaw hotel room, the same officer was woken again by head pain he rated nine or 10 on the pain scale - worse than in London. He described the sensation as someone standing over him repeatedly hitting him on the head with a baseball bat, and in the years that followed he suffered chronic nerve pain, fatigue and severe health problems.

Sources described him as a senior CIA officer who had recently been given an important job relating to worldwide operations against Russia.

From Havana to anomalous health incidents

The condition takes its name from Havana, where mass reports first emerged among US diplomats in Cuba who believed they may have been attacked with a sonic weapon - two years before the officer's London night. In official documents the episodes are called anomalous health incidents, or AHIs.

Explanations have always split along institutional lines:

• •Many CIA officers believed AHIs came from a Russian intelligence operation using an unknown weapon delivering sonic or pulsed microwave energy.
• •Some scientists called a portable weapon science fiction and pointed instead to environmental factors, toxins, chirping crickets or mass hysteria.
• •Some within the CIA alleged that victims were faking symptoms for a medical payout.

Official findings flip: genuine cases, no adversary, then a reversal

In 2022, a US government-convened panel of scientific experts concluded that "the signs and symptoms of AHIs are genuine and compelling" and could be due to external stimuli.

A year later the intelligence community swung the other way. Its unclassified summary stated that "The available intelligence consistently points against the involvement of US adversaries in causing the reported incidents" and called a Russian campaign very unlikely. This summer, Donald Trump's outgoing director of national intelligence rescinded that assessment, claiming it rested on flawed analysis.

The 60 Minutes book and the evidence behind it

Michael Rey and Oriana Zill de Granados, longtime producers for CBS's 60 Minutes, have covered the story from the start and are now releasing a book arguing that Russia was behind at least some episodes - and accusing parts of the US government and intelligence community of covering up the evidence.

David Relman, the Stanford professor who led the 2022 scientific panel, said a subset of cases was "most plausibly explained by exposure to pulsed microwave energy". His panel reviewed patient records and more than 1,000 classified documents, and Relman said that "it inevitably leads to the conclusion that there may have been a cover-up".

The producers first encountered the story a decade ago, when they covered the Obama administration's 2015 re-establishment of diplomatic relations with Cuba. When reports of the condition surfaced at the reopened Havana embassy the following year, a senior US diplomat confirmed the reports to Zill and offered contacts.

They then spoke to more than a dozen Havana victims off the record, and by the time they prepared a story, similar cases were appearing among US diplomats in China and then worldwide. After their first 60 Minutes episodes aired, victims including current or former undercover CIA officers got in touch - people across the world who did not know each other told remarkably similar stories.

A pattern ran through the key cases. Alleged victims had worked on beats touching Russian interests, and several locations were Moscow-allied places where elites wanted better western relations - Cuba during the Obama-era thaw, but also Georgia, Kyrgyzstan, Serbia and Vietnam. Several CIA officers stationed in Kyiv around the 2014 Maidan revolution, which Vladimir Putin decried as a US-backed coup, later suffered AHIs in different locations across the world.

The book's cornerstone case predates Cuba. Mike Beck, an NSA counter-intelligence officer, fell ill in the 1990s while on temporary assignment checking a US diplomatic facility for bugs. He developed a rare form of Parkinson's disease at 45 and died this year.

A declassified NSA statement in Beck's 2014 workplace compensation claim cited 2012 intelligence linking the hostile country he had travelled to - identified by sources as Russia - with "a high-powered microwave system weapon that may have the ability to weaken, intimidate or kill an enemy" over time without leaving evidence.

Rey and Zill also document what they call the first known contemporary AHIs. In late 2014, several US government employees at the consulate in Frankfurt, Germany, fell ill, and one was found unconscious in a stairwell after feeling sudden, intense pressure on her chest and hearing a high-pitched squeal.

In 2015, a US defence institute researcher toured the Balkans with defence attaches, passing through Montenegro, then applying for Nato membership, and Serbia, a Russian ally resentful over the 1999 Nato bombing of Yugoslavia. On her final evening in Belgrade she felt a sinking sensation like being in a suddenly descending lift, and saw her government laptop flicker with blue static and never work again.

In the following weeks she felt weak, struggled to speak clearly, and developed pain she described as "like a drill was going into my eye". She burned through vacation, sick and donated leave and eventually left her job, only later connecting it to Havana syndrome reports.

Marc Polymeropoulos, a Middle East veteran, was made deputy chief of operations for Europe and Eurasia in 2017 as the CIA pushed back against Moscow's intelligence agencies. He said the agency "wanted us to take the same kind of tactics and spirit we used in the global war on terror to the Russians" - even as Trump publicly denied Russian interference in the 2016 election.

On a liaison trip to Moscow in early December 2017, Polymeropoulos and another senior CIA executive met SVR and FSB counterparts; the meetings were ill-tempered and lacking in substance. Late that night he woke with vertigo and a splitting headache. "I had vertigo and a splitting headache. I thought it was food poisoning at first," he said, before realising the room was spinning and his ears were ringing.

Rey said that the more source meetings the producers held, the more they felt something real was behind the reports: the people coming forward were highly effective intelligence officers, all telling versions of the same story. Zill, for her part, said she went through years of doubts.

The 2023 intelligence assessment that a foreign campaign was "very unlikely" has now been rescinded, and the journalists' book argues Russia stood behind at least some episodes while accusing parts of the US government of covering up the evidence.