Toyota Motor Corp.'s request to seal a U.S. lawsuit by a former in-house attorney claiming the carmaker destroyed crash data was denied Thursday by a judge who said the suit was already "irreversibly" public.

The suit, filed in July by Dimitrios Biller, a former Toyota in-house lawyer, claims the automaker hid engineering and testing results in more than 300 car-rollover cases. The company is "disappointed" with the decision, said Mike Michels, a Toyota spokesman.

"We remain confident that we have acted appropriately in product liability cases and in all reporting to federal safety regulators," Michels said. "The court's decision does not affect the fundamental aspects of the case in any way."

The dispute adds to U.S. challenges for the company and new President Akio Toyoda, who has vowed to put Toyota "back on the right track" after a record loss and forecast of a bigger deficit this year. The U.S. recession and plunging demand led Toyota to idle a Mississippi plant that was to open in 2010 and end a U.S. joint venture factory shared with General Motors Corp. for 25 years.

"Anything that involves questions of safety and a cover up, that's bad," said Michael Schmall, managing partner for Planning Edge, a Birmingham, Mich.-based market-research firm. "Just the fact that the allegations are out there hurts."