The mother of a university student who died of carbon monoxide poisoning in 2005 accused Paloma Industries Ltd. and parent Paloma Co. of failing to stop unauthorized modifications of their gas-powered water heaters that they knew were defective, as the manufacturer's Tokyo District Court negligence suit opened Thursday.

Yukiko Joshima told the court: "If Paloma's product hadn't been defective, Hiroyuki wouldn't have died. Paloma took away the happiness of our family."

Hiroyuki Joshima, 18, died of carbon monoxide poisoning in November 2005 when he used a modified Paloma water heater at his condominium in Minato Ward, Tokyo. His older brother, Takayuki, was also poisoned and had to be hospitalized for about a month.

The family filed the suit against Paloma, Tokyo Gas Co. and a maintenance company in November seeking about ¥200 million in compensation, claiming they could have prevented the accident but neglected to do so.

Paloma rejects the claim, arguing that it is not responsible for unauthorized modifications.

Former Paloma President Toshihiro Kobayashi was charged in December with professional negligence resulting in death and injury, and failure to take measures to prevent accidents.

Joshima said she was told by police when Kobayashi was indicted that the modification was done by a maintenance company worker who has since died of cancer. During the investigation, the worker reportedly admitted modifying the heater at the student's condo in 1995.

From 1985 to 2005, Paloma water heaters were reportedly involved in 28 cases of carbon monoxide poisoning resulting in 21 deaths.

In many of the cases, the water heaters had solder fractures that repair personnel circumvented rather than fixed by modifying safety devices, which caused the heaters to operate without their fans, according to earlier reports.

In December 2006, Paloma acknowledged the incidents occurred due to product defects.

"It's not about money. It's about them facing this issue with sincerity," Joshima said. "We just want to know the truth and clarify the responsibilities."