Three former top executives at Tokyo Electric pleaded not guilty Friday to charges related to the triple core meltdown at the Fukushima No. 1 nuclear power plant in 2011, which forced at least 150,000 people to evacuate and caused considerable damage to the prefecture’s economy.

The trial, which opened Friday at the Tokyo District Court, is the first in which criminal charges have been pressed in connection with the Fukushima disaster.

Facing massive liabilities, the utility received a government bailout and was restructured into Tokyo Electric Power Company Holdings Inc. It is better known as Tepco.

Criminal complaints against more than 50 state and Tepco officials have been filed by residents of Fukushima and other people since 2012.

On trial are ex-Tepco chairman Tsunehisa Katsumata, 77, and former Vice Presidents Sakae Muto, 67, and Ichiro Takekuro, 71. The three are being charged with professional negligence resulting in death and injury.

The charges are linked to the deaths of about 40 patients at Futaba Hospital in the town of Futaba who were forced to flee the Fukushima area and later died.

The trial was set when a previous judgment by prosecutors not to pursue charges was overturned by an Inquest of Prosecution — a rare procedure that can be used to appeal such a decision before a panel of ordinary citizens.

According to a court spokeswoman, a line of more than 700 people began forming at 7:30 a.m. for a chance to witness the trial and 54 were let in.

During Friday’s trial session, the three former executives apologized but maintained that it was impossible to foresee the giant tsunami that swamped the plant on March 11, 2011.

“I apologize for causing the serious accident,” said Katsumata, before adding that “it was impossible to predict.”

However, a government report published in 2011 concluded that Tepco was aware that a 15.7-meter-high tsunami could hit the plant if a giant quake occurred off the coast of Fukushima, based on a simulation in 2008 that modeled the impact of a tsunami on the plant, whose seawall was woefully overmatched by the powerful waves.

The 2002 estimate by the government’s Headquarters for Earthquake Research Promotion also estimated that there was a 20 percent chance of a magnitude 8 earthquake striking off Fukushima within 30 years.

The 2008 data were relayed to Takekuro and Muto, who were in charge of Tepco’s nuclear business at that time, and were also “very likely” to have been reported to Katsumata by June 2009 at the latest, according to an independent committee of citizens that reviewed the prosecutors’ decision not to press charges.

In court Friday, however, Katsumata told prosecutors that he has “no memory of having been briefed” on the information.

The main reason prosecutors had decided not to pursue a criminal case was their belief that the nuclear accident was unavoidable, even if the three had decided to introduce tsunami countermeasures based on the 2008 data.

The simulation suggested the need to build a seawall on the south side of the plant, covering a portion of coastline about 300 meters long. But in March 2011, tsunami reaching heights of around 14 to 15 meters impacted the east side of the plant, which faces the Pacific Ocean, swamping a far longer stretch of coastline.

As the hearing opened, a group that had pushed for the trial met at the House of Councilors, to share their experiences from the nuclear disaster with others and express their views on Tepco.

“I’m glad that the first hearing was finally held. We finally (came) all this way, and this is our true beginning,” said Miwa Chiwaki, one of the members of the group.

Named the Complainants for the Criminal Prosecution of the Fukushima Nuclear Disaster, the group had been submitting criminal complaints to prosecutors since June 2012, but it wasn’t until July 2015 that mandatory indictment for the three former executives was approved.

“No one has been held responsible so far, and the true background information of the Fukushima nuclear disaster remains unclear,” Chiwaki said.

Another speaker, Yui Kimura, said the blame rests with them: “They hide behind their job titles, and don’t accept their responsibilities as people.”

The triple meltdown in 2011 was the world’s worst nuclear disaster since Chernobyl in 1986. It forced about 80,000 residents of the prefecture to leave their homes, many of them for good.

The 2011 mega-quake, tsunami and nuclear disaster left some 18,500 people dead or missing, but Tepco’s plants have not been officially blamed for causing any of the deaths.

“I know that this trial could become great motivation for the other trials (involving Tepco) taking place nationwide,” said Chiwaki.

Information from Kyodo added