ROME — Seven scientists and other experts went on trial on manslaughter charges Tuesday for allegedly failing to warn residents sufficiently before a devastating 2009 earthquake that killed more than 300 people in central Italy.

The case is being closely watched by seismologists around the globe who insist it's impossible to predict earthquakes and dangerous to suggest otherwise, since they will be discouraged from issuing any advice if they fear legal retaliation.

Last year, about 5,200 international researchers signed a petition supporting the scientists. The Seismological Society of America wrote to Italy's president expressing concern about what it called an unprecedented legal attack on science.

The seven defendants are accused of giving "inexact, incomplete and contradictory information" about whether smaller tremors felt by L'Aquila residents in the six months before the April 6, 2009, quake should have prompted a quake warning.

"We all know well that earthquakes cannot be predicted. This is not in the point here," said Vincenzo Vittorini, a relative of a victim, who attended the trial.

Rather, he said, because of the failure of the scientists to say a significant quake could be possible, victims and their relatives missed a chance to take preventive measures.

Prosecutors focused on a memo issued after a meeting on mounting concerns about the months of seismic activity in the region. Released a week before the big quake, it concluded it was "improbable" there would be a major quake, though it added that one couldn't be excluded.