"Claims such as these have raised additional concerns about Takata's handling of airbag issues and are one of the reasons we're compelling them to produce documents and answer questions, under oath," the highway safety agency said.
"Takata will continue to fully cooperate with the government investigation as we also support the needs of our customers," Mr. Berman, the spokesman, said.
Read MoreUncertainty to push Takata to wider loss
In Tokyo on Thursday, the company's chief financial officer apologized broadly for the problems caused by the defective airbags, while the company announced that legal uncertainty and rising recall costs would result in a larger-than-expected quarterly loss.
"We don't know at this point how things will play out," said Yoichiro Nomura, the chief financial officer.
The most recent death linked to the airbags involved an accident in a suburban Los Angeles parking lot last year. Hai Ming Xu, 47, was killed by an airbag that deployed explosively in his 2002 Acura TL.
The police in Alhambra, Calif., initially treated the case as a homicide because of the nature of his injuries, before an autopsy suggested the wounds were caused by the airbag, according to a Los Angeles County Coroner's report. The report concluded that extensive lacerations on Mr. Xu's face came from "a metallic portion" of the airbag inflater that "hit the deceased on the face as it deployed." The report also said tears had been discovered in the airbag.
The first known rupture of a Takata airbag occurred in Alabama in 2004, according to Honda. The inflater that ruptured in the Accord and injured the car's driver that year "looked like it had exploded, and had a hole punched out of the side of the canister," said one of the former Takata lab employees who examined the airbag.
Takata and Honda have declined to disclose further details of that accident, which ended in a settlement between the automaker and the driver, according to Honda.
Behind the scenes, however, the former Takata lab employees said, the manufacturer wanted to know more. The tests on the 50 airbags were supervised by Al Bernat, then Takata's vice president for engineering, they said, and were unknown to all but a small group of people, that included lab technicians, fabricators and engineers. The employees said that they did not know under whose authority Mr. Bernat was operating.
The tests' results worried the technicians: Two of the airbag inflaters Takata had retrieved from the junkyards showed cracks and the start of "rapid disassembly" during the tests, Takata's preferred term for explosion, according to the two people. They said Takata engineers at the time theorized that a problem with the welding of the inflater's canister, intended to hold the airbag's explosives, made its structure vulnerable to splitting and rupturing. The two people said engineers designed prototypes for possible fixes, including a second canister to strengthen the unit.
But after three months, they said, the testing was ordered halted. The lab employees were also instructed that all data, including video and computer backups, be destroyed. Inflaters and prototypes of fixes were also to be disassembled and disposed of in a scrap-metal Dumpster, the senior lab employee said. No explanation was offered, the employee said, though the order was not considered surprising given the secret nature of the testing.
Read MoreAudi recalls nearly 102,000 vehicles to fix air bag
As for the two problematic airbag inflaters, Mr. Bernat, the supervisor, told people at the time that they were not significant because they had been retrieved from cars with cracked windshields and were likely "corrupted by weather," according to the two former employees.
Reached at his home in Rochester Hills, Mich., Mr. Bernat declined to comment and referred questions to his former employer. Takata also declined to comment.
As automakers have recalled the airbags in recent years, Takata has suggested that weather plays a significant role in making its airbags prone to rupture. Takata said humidity could hurt the stability of the airbag's explosives.
In explaining the efect, the company has also pointed to manufacturing flaws involving the airbags' explosive, or propellant, including improper exposure to moisture, and problems with a machine that presses propellant powder into tablets. Takata has said both troubles were corrected in the early 2000s.
But the internal documents suggest Takata engineers scrambled as late as 2009 to repair a machine at its Monclova plant that pressed explosive propellant powder into pellets after "inflaters tested from multiple propellant lots showed aggressive ballistics," according to the internal presentation in June 2009.
The internal materials and interviews with the former quality-control managers also suggest that quality control problems at Takata stretched beyond its production lines.
Airbag modules would get wet during transit, arriving wet at automakers' assembly plants on leaky trucks, the managers said. The problems were addressed in an overhaul of operations at the plant starting in 2004, but local managers struggled to maintain the stricter controls.