An engineer at General Motors who is at the center of accusations that the company covered up a deadly defect appeared distraught during lengthy questioning by congressional investigators, according to people familiar with the session.
The engineer, Raymond DeGiorgio, who was suspended last month with pay, has not spoken publicly since G.M. acknowledged the ignition switch defect in February and began recalling millions of Chevrolet Cobalts, Saturn Ions and other models. The automaker has linked the defect to 13 deaths, a number that federal regulators said was expected to grow.
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A House staff aide said that Mr. DeGiorgio, 61, appeared "genuinely upset" about the deaths and about his inability to connect the ignition switch problem with the failure of air bags to deploy.
The defective switch could cause engines to shut down, disabling electrical systems and things like power steering, power brakes and air bags. Mr. DeGiorgio, who has worked at G.M. since 1991, was a lead design engineer for ignition switches for a variety of models.
"He came across as if he was just overburdened and just missed it," said the staff member, who was not authorized to speak publicly about the investigation. Mr. DeGiorgio's comments, during 10 hours of questioning on May 19, offer a glimpse into how the switch was secretly changed eight years ago, but no recall was issued for vehicles equipped with the defective switches until this February.
Mr. DeGiorgio did not give any information that indicated that the new chief executive of G.M., Mary T. Barra, knew anything about the problem before she took her job early this year. He did not seek to implicate any of his superiors, the people familiar with the questioning said.
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Mr. DeGiorgio was asked about statements he made during a deposition last year in a wrongful-death lawsuit brought against G.M. Mr. DeGiorgio told the congressional investigators that when giving that deposition, he had forgotten his decision to order a major upgrade in the switch, according to the people familiar with the session.
Mr. DeGiorgio signed off on changes in the ignition switch in April 2006, authorizing a supplier, Delphi, to make improvements to the switch at its manufacturing plant in Mexico. But he denied it in the deposition last year in the lawsuit, which was brought by the family of a Georgia woman who died in a 2005 Chevrolet Cobalt.
"I don't ever recall authorizing such a change," he said in a sworn deposition in April 2013.
Under questioning by the House investigators, Mr. DeGiorgio said he had forgotten about the fix — which involved a stronger spring in the mechanism that determines how much force is needed to turn the key — because it was one of a package of changes, and because it was seven years before the deposition, according to the people familiar with the questioning.
Mr. DeGiorgio was not sworn in, but speaking untruthfully in such settings can carry substantial legal penalties, according to experts.
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The change he approved covered two items, the spring and a printed circuit board, known as a P.C.B., that was causing some Saturn Ion models not to start, according to one person involved in the case.
"He definitely said he was more focused on electrical problems" said the staff member, who described Mr. DeGiorgio as "very emotional at times."
Mr. DeGiorgio's actions might not have come to light without an independent investigation by a Florida engineer, Mark Hood, who was retained by the family of the Georgia woman, Brooke Melton.
Mr. Hood discovered that switches in Cobalts made after 2006 were significantly stronger than ones found in pre-2006 cars.
He was pressed on that point by Lance Cooper, the lawyer for the Melton family during the deposition last year.
"So if any such change is made, it was made without your knowledge and authorization?" Mr. Cooper asked.
"That is correct," Mr. DeGiorgio said.
The Meltons have asked that their case against G.M. be reopened on the grounds that Mr. DeGiorgio possibly committed perjury, because it appeared that he gave a false answer in the deposition last year.
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Ms. Barra, the chief executive, acknowledged under questioning by lawmakers on April 2 that Mr. DeGiorgio might have lied during his deposition.
"You know he lied under oath," said Senator Claire McCaskill, Democrat of Missouri.
"The data that's been put in front of me indicates that, but I'm waiting for the full investigation," Ms. Barra said.
Eight days later, on April 10, Mr. DeGiorgio was suspended with pay by G.M. along with his supervisor, Gary Altman. House investigators have also interviewed Mr. Altman. Mr. DeGiorgio has not returned telephone calls to his home in a rural suburb of Detroit.
Interviews by House investigators are often a preliminary step to calling witnesses for a public hearing, although the House committee undertaking the investigation, Energy and Commerce, has not scheduled a hearing.
—By Matthew L. Wald and Bill Vlasic, New York Times