Naoto Kan, Japan's prime minister when the disaster occurred last year, told the Australian Broadcasting Corp. that an audio recordings of an exchange between him and executives with the plant's operator, Tokyo Electric Power Co., are "crucial."
"This is extremely important material which is needed to investigate the cause of this accident," Kan told ABC in an exclusive interview.
"It's like the black box flight recorder on an [airplane]. The black box is crucial to understanding how an accident happened. So too are these recordings."
ABC said Tepco had agreed to release numerous hours of teleconference video from the days after the disaster at the plant after refusing to do so, citing privacy of those on the recordings. But Tepco acknowledged audio of the exchange with Kan is missing and blamed lack of hard drive disc space.
ABC said the recordings could provide information on whether Tepco wanted to withdraw its workers from the plant during its early handling of the crisis, as Kan has maintained.
"The most contentious issue is whether or not Tepco was planning to abandon the Fukushima plant," Kan said.
"The audio and video will make it clear what discussions Tepco was having about withdrawing."
ABC said the audio recordings of the exchange also could shed light on allegations Kan had meddled, delaying Tepco's response.
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