Six years after a deadly explosion ripped through a spa in Tokyo’s bustling Shibuya district, the facility’s chief designer was found guilty Thursday of professional negligence resulting in death.

Yoshihiko Tsunoda, 55, a designer-in-charge at leading contractor Taisei Corp., was sentenced to three years in prison, suspended for five years.

Three employees, all women, were killed in the blast at women-only Shiespa in June 2007. Three people passing by were severely injured, including one who remains partially paralyzed.

Hiroyuki Sugahara, 50, a board member of Unimat Fudosan K.K., the real estate company that owned the spa, was meanwhile found innocent by the Tokyo District Court.

The explosion occurred when methane gas built up in the spa’s machinery room, investigators found. Although it had a discharge pipe to let the gas escape, it was clogged by condensation. The pent-up gas found its way into the machinery room, where a spark touched it off.

While designing the facility, Tsunoda decided to use a U-shaped discharge pipe out of consideration for neighboring residents. The pipe had a valve spa staff were supposed to use occasionally to release the condensation.

But Tsunoda, despite being fully aware how important this process was, did not explain it directly to Unimat. The valve ended up never being touched.

“The defendant neglected to fulfill his accountability in a proper manner, which led to the accident,” presiding Judge Takashi Tawada said.

Tawada said Sugahara can’t be held accountable because he is not an architect.

Nobuyuki Senzai, 66, whose 23-year-old daughter, Akina, was killed in the blast, said after the ruling he was satisfied to learn Sugahara was found innocent as he had repeatedly apologized sincerely to the victims’ kin.

Senzai was also displeased by the way the trial dragged on. He blamed Taisei and its reluctance to admit culpability.

“If Unimat was the main party we were litigating against, I don’t think we would have waited this long to hear the ruling,” Senzai said. “I think this is an example of the huge influence a major contractor can wield.”

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