Six Italian scientists and a government official were found guilty on Monday of multiple manslaughter for underestimating the risks of a killer earthquake in the town of L'Aquila in 2009.
They were sentenced to six years in jail in the watershed ruling in a case that has provoked outrage in the international science community.
Some commentators had warned that any convictions would dissuade other experts from sharing their expertise for fear of legal retribution.
Prosecutor Fabio Picuti had asked for jail sentences of four years for each defendant for failing to alert the population of the walled medieval town of L'Aquila to the risks, days before the 6.3-magnitude quake killed 309 people.
All seven were members of the Major Risks Committee which met in the central Italian town on March 31, 2009 - six days before the quake devastated the region, tearing down houses and churches and leaving thousands homeless.
Picuti on Monday compared the committee to the US Federal Emergency Management Agency (FEMA), which was castigated for failing to assess the risks before Hurricane Katrina devastated New Orleans in 2005.
FEMA head Michael Brown resigned in the wake of the disaster, and Picuti blamed a similar "failure of initiative" to forecast the risks for L'Aquila.
But Alfredo Biondi, the lawyer for expert Claudio Eva, had rejected his claim, saying: "While floods and hurricanes can be forecast, earthquakes cannot."
The bright blue, classroom-sized temporary tribunal in L'Aquila - built on an industrial estate after the town's historic court was flattened in the quake - was crowded with dozens of lawyers, advisers and international media for the verdict.
Four of the defendants were in court, as well as a small group of survivors.
"They were not expected to predict the earthquake but they were expected to alert people to the risks," said lawyer Wania dell Vigna, who represents 11 plaintiffs, including an Israeli student who died when a student residence collapsed.
Aldo Scimia, whose mother was killed, said: "Their main duty is to provide security, and they failed."
Another relative of one of the victims who gave her name only as Ortense said her sister had died because "she was reassured by the experts and slept at home that night."
In his summing up, Picuti said the experts had provided ‘an incomplete, inept, unsuitable and criminally mistaken’ analysis, which reassured locals and led many to stay indoors when the first tremors hit.
The government committee met after a series of small tremors in the preceding weeks had sown panic among local inhabitants - particularly after a resident began making worrying unofficial earthquake predictions.
Italy's top seismologists were called in to evaluate the situation and the then vice-director of the Civil Protection agency, Bernardo De Bernardinis, gave press interviews saying the seismic activity in L'Aquila posed ‘no danger.’
"The scientific community continues to assure me that, to the contrary, it's a favourable situation because of the continuous discharge of energy," he said.
The claim that shocks discharge energy and reduce quake risks has been disputed and the scientists deny having told Bernardinis anything of the sort.
The prosecution had accused Bernardinis of using the meeting to calm the residents -- he famously advised them to relax with a glass of wine.
Medieval criminal law
Government lawyer Carlo Sica, who had called for the seven defendants to be acquitted, said that minutes from the March 31 meeting were not valid as evidence because they were only written up and signed after the April 6 earthquake.
"They are not guilty of anything, the earthquake's no one's fault," he said.
Filippo Dinacci, lawyer for Mauro Dolce and Bernardinis, had criticised the charges last week as something out of "medieval criminal law."
The case sparked outrage in the international scientific community when the charges were brought against the geophysicists in 2010, with many complaining that they were merely scapegoats and warning against putting science on trial.
Over 5,000 members of the scientific community sent an open letter to President Giorgio Napolitano denouncing the trial against colleagues for failing to predict an earthquake -- a feat widely acknowledged to be impossible.
The seven include Enzo Boschi, who at the time was the head of Italy's national geophysics institute; Giulio Selvaggi, head of the INGV's national earthquake centre in Rome, and Franco Barberi from Rome's University Three.
The other scientists on trial are Mauro Dolce, head of the Civil Protection's seismic risk office; Gian Michele Calvi, head of the European centre of earthquake engineering; and Claudio Eva from the University of Genoa.
About 120,000 people were affected by the quake, which destroyed the city's historic centre and medieval churches as well as surrounding villages.
As well as the manslaughter charge, the seven have been accused of reckless endangerment, causing buildings to collapse with serious injury to people.