TOKYO - A Japanese court on Thursday found three former executives of Tokyo Electric Power Co. not guilty of professional negligence over the 2011 tsunami- induced reactor meltdowns at the Fukushima Daiichi nuclear power plant.

Former Tepco chairman Tsunehisa Katsumata, 79, and two former colleagues were accused of failing to take adequate precautions to safeguard the plant against the 9.0-magnitude earthquake and tsunami that struck the region on March 11, 2011. The disaster crippled the plant and spread radioactive contamination across a swath of northern Japan.

The trial at Tokyo's District Court marked the only criminal proceedings resulting from the nuclear explosions and meltdown, which forced the evacuation of more than 165,000 people. Tens of thousands are still prevented from returning because of lingering contamination.

The court also found the trio not guilty of causing the deaths of 44 elderly patients who were forcibly evacuated from hospitals.

Government scientists had warned years earlier of a significant risk of an earthquake and tsunami along Japan's northeastern coast, imperiling the plant. But the three men argued that they could not have predicted such a massive tsunami, an argument ultimately accepted by the court.

"It would be impossible to operate a nuclear plant if operators are obliged to predict every possibility about a tsunami and take necessary measures," Judge Kenichi Nagafuchi said in handing down the ruling.

The Fukushima meltdown was the world's worst nuclear accident since the 1986 Chernobyl disaster in the former Soviet Union, and it caused a reevaluation of the risks of nuclear power globally, especially in Germany.

Japan's government shut down the country's 50 other nuclear reactors after the disaster and imposed new safety rules. But in recent years it has reopened nine, with the government of Prime Minister Shinzo Abe pushing to restart more, partly to reduce Japan's reliance on fossil fuels but also because the nuclear lobby retains considerable influence within the corridors of power, experts say.

Prosecution lawyers, who had sought jail sentences of five years, said they will consider whether to appeal the ruling, arguing that the verdict was influenced by the government's policy on nuclear energy.

"The ruling says absolute safety is not a requirement," prosecution lawyer Shozaburo Ishida said at a news conference. "That's unthinkable. If you believe that a nuclear accident should never happen, you wouldn't hand down this sort of ruling."

There was anger at the verdict outside the courtroom, where former residents of the affected area and activists had gathered. The legal action, brought by former residents, was delayed for years after prosecutors twice refused to bring a case.

"It's like the court is on Tepco's side," said Noboru Honda, a community leader who lost his home and livelihood after the disaster. He described the victims as "stunned" and "indignant" to hear the accident being described as a natural disaster and not the result of human error by Tepco officials.

"They built the plants and bear no responsibility? What about us? Our pain? We had to move nine or 10 times. Even today, families live apart, and we are living a tough life. Where can we direct our indignation?"

Greenpeace condemned the court's decision, arguing that Japan's legal system had failed to stand up for the rights of people affected by the meltdown.

"A guilty verdict would have been a devastating blow not just to Tepco but the Abe government and the Japanese nuclear industry. It is therefore perhaps not a surprise that the court has failed to rule based on the evidence," Shaun Burnie, a senior nuclear specialist at Greenpeace, said in a statement. "More than eight years after the start of this catastrophe, Tepco and the government are still avoiding being held to full account for their decades of ignoring the science of nuclear risks."

Efforts to restart Japan's nuclear plants have been dogged by safety concerns, tougher regulations and local opposition around the plants, making it unlikely that the government will achieve its target for nuclear energy to supply 20 to 22 percent of the country's power by 2030.

Muneyuki Shindo, a professor emeritus at Chiba University and critic of Japan's nuclear regulatory oversight, said the verdict reflected "mainstream thinking" that nuclear power is here to stay despite the risks and raised questions about the independence of the judiciary.

But he said the fact that so many internal documents were revealed during the trial could make regulators more cautious about approving other restarts in future.

The court heard evidence that Tepco executives were warned between 2002 and 2008 that there was a 20 percent chance that an earthquake greater than 8-magnitude could occur off Japan's east coast in the next three decades, potentially triggering a tsunami significantly higher than the sea wall protecting the plant.

But the company failed to invest in measures that might have prevented the catastrophe, such as raising the height of the sea wall and installing additional emergency generators.

The 30-foot-high tsunami that followed the earthquake flooded the plant and knocked out the electric power that cooled the reactors, causing explosions and reactor meltdowns.

Executives, struggling with losses from the shutdown of another nuclear plant after an earthquake in Niigata in 2007, were accused of delaying preventive action for cost reasons, but they argued they had not acted because they had considered the warnings unreliable.

"We once again offer our sincerest apologies for causing great trouble and worries to many people, including people in Fukushima Prefecture," Tepco said in a statement after the ruling.

The majority-state-owned company said it was "putting all efforts" into Fukushima's reconstruction, providing compensation for disaster-related damage and carrying out decommissioning work and decontamination. It added that it was determined to reinforce security measures at nuclear power plants.

But the verdict, and the implication that the nuclear power operators cannot be blamed for accidents that may occur, is unlikely to help restore shaky public trust in the industry - especially in a country where earthquakes and tsunamis are common.

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The Washington Post's Akiko Kashiwagi contributed to this report.

This article was written by Simon Denyer, a reporter for The Washington Post.