US President Donald Trump said last week he believed Havana was responsible for 24 diplomats being harmed. Washington expelled 15 Cuban diplomats and recalled more than half the US diplomatic personnel from Havana earlier in October.
While Cuba denounced the expulsions as "unjustified" and accused the United States of insufficient cooperation, three Interior Ministry officials and a doctor heading the inquiry provided more details in an interview in Havana on Sunday.
Cuba had deployed about 2,000 security officials and experts, from criminologists to audiologists and mathematicians, to investigate the incidents after it became aware of them in February, the investigators said.
The probe has not ended but so far has failed to uncover any evidence to corroborate allegations of attacks that the United States says have caused hearing loss, dizziness, fatigue and cognitive issues for diplomatic personnel who were based on the Communist-run island.
"This is slander by the United States," said Coronel Ramiro Ramirez, responsible for the security of diplomats in Cuba.
Asked to respond to the Cuban officials' assertions, State Department spokeswoman Heather Nauert said the United States had reminded Cuba of its obligation to ensure the safety of US diplomatic personnel and was continuing its investigation of the "attacks."
Washington officials have raised the possibility that sonic weapons were used to harm the diplomats, according to US media reports. However, Cuban investigators denied such weapons could even have been used by third parties without affecting the health of others or attracting attention.
"It's impossible. We are talking about science fiction," said Lieutenant Colonel Jose Alazo, an expert in the criminal investigation unit of the Interior Ministry. "From a technical point of view, that argument is unsustainable."
Hard to explain
The investigators said the United States had supplied 14 recordings of the sound it says the victims heard during the attacks and recorded, for example, on cellphones.
These, however, did not contain anything that could damage human health, they concluded. The noises included the usual suburban sounds such as traffic, footsteps and voices.
They were also characterized by a deviation peak of 7 kiloHertz (kHz) in the frequency band of 3 kHz, similar to the song of a cricket.
An audible sound would need to be very loud - above 80 decibels or akin to a plane's engine - to have a health impact, they said. Yet only the victims heard the noise, not their families living in the same houses, or their neighbors.
"We interviewed more than 300 people in the neighborhood, we also evaluated more than 30 medically, and no one heard these things," Alazo said.
Even if the US diplomats' reports of loud sounds were misleading and the source of the attacks was infra- or ultrasonic and therefore inaudible to human ears, it would be hard to explain how it could go undetected, the Cuban investigators said.
"You would need a source that could be seen from a satellite, it would be enormous," said Dr Manuel Villar, an ear, nose and throat specialist.
Finally, only two or three of the alleged victims had hearing problems, according to the US information provided, whereas any kind of sonic attack would cause them in everyone, Villar said.
'Anti-Cuban mafia'
The United States has not formally accused Cuba of carrying out attacks, but Trump's comments further damaged relations between the old Cold War foes, which have rapidly deteriorated since he took office.
Canada has said several Canadians had reported similar symptoms to the US diplomats but it has not taken any action against Cuba and has said Cuba had been very cooperative with the investigation.
"There is an anti-Cuban mafia in Miami and we are victims of their dirty work that involve certain people very close to the governing circles of the United States," Ramirez said.
Anti-Castro Cuban-Americans such as Republican Senator Marco Rubio of Florida have guided Trump's policy on Cuba, including a partial rollback of the historic detente forged by Trump's Democratic predecessor Barack Obama.
Washington insists its drawdown at its embassy was motivated by concern for the health of its diplomats.
"The safety and wellbeing of American citizens is our top priority," said Nauert.
Investigators said US actions did not add up with their accusations. More than 200 friends and relatives of US diplomats based in Havana had asked for visas to visit them between February and July, despite the alleged attacks.
The fact that the information the United States provided was late was a major obstacle to resolving the mystery, said the investigators, who declined to comment on the state of cooperation with Canada.
So far, Washington had only officially reported 14 cases of alleged attacks to Cuba, compared with the 24 it had announced to the media, they said.
"It will be impossible to resolve this investigation without more cooperation," Ramirez said.
