A U.S. congressional probe on Monday looked at why General Motors employees repeatedly approved ignition switches that failed to meet company standards and how those decisions may have contributed to crashes linked to at least 13 deaths.
Lawmakers are also exploring whether another 14 fatalities could be connected to the faulty ignition switches.
Democrats on the House Energy and Commerce Committee released details of some of the more than 200,000 pages of documents they have received from GM and a federal regulator.
The release added to information contained in a parallel memo issued on Sunday by Republicans on the committee, ahead of a high-profile hearing Tuesday about GM's recall of 2.6 million vehicles.
The recalled vehicles could have defective ignition switches that cause their engines to stall during operation, which also disables airbags, power steering and power brakes.
Lawmakers are trying to piece together why it took GM more than a decade to issue the recalls, despite repeated red flags.
On Monday, questions were already beginning to surface about whether more deaths could be linked to the ignition switch problem.
Democrats cited data from the National Highway Traffic Safety Administration (NHTSA) regarding 14 other deaths in newer models of the recalled cars. Those deaths occurred in accidents with vehicles displaying some of the same problems as those in the earlier fatalities.
The 14 deaths occurred after the 13 fatalities that GM has connected to defective ignition switches.
Lawmakers also noted inconsistencies regarding the role of a key GM engineer, Ray DeGiorgio, over a 2006 decision to revise the design of the ignition switch.
In an April 2013 deposition related to a crash in Georgia involving a recalled GM car, DeGiorgio said the company "certainly did not approve a detent plunger design change" for the 2006 replacement ignition switches.
However, California's Rep. Henry Waxman and other senior Democrats on the House Energy and Commerce Committee said on Monday that "GM has provided the panel with documentation verifying that a Ray DeGiorgio, lead design engineer for the Cobalt ignition switch, signed off on a Delphi ignition switch change on April 26, 2006."
GM declined to make DeGiorgio available for comment on Monday.
GM officials were looking into the design of the ignition switches by 2001, according to the documents.
The manufacturer of the switch, Delphi Automotive, said the redesigned switches used in 2008-2011 models of the recalled GM vehicles still did not meet GM standards, according to the records. That is an assertion that could increase the number of deaths linked to the defect.
"An analysis of NHTSA early warning report data shows that there are 14 fatal crashes in the recalled 2008-2011 vehicles involving a potential problem with an airbag, steering, electrical or unknown component," senior Democrats on the House Energy and Commerce Committee said.
Waxman and Reps. Diana DeGette (D-CO) and Jan Schakowsky (D-IL), all on the Oversight and Investigations subcommittee, said: "This information raises important new questions about what GM knew, when GM knew about the risks from this faulty ignition switch, and how the company has handled the recalls of affected vehicles, including the recall of the 2008-2011 model year vehicles that was announced just three days ago."
Compounding its concerns in Washington, GM was previously forced to recall 4.8 million automobiles for repairs in March.
Late Friday, GM also announced it would recall 490,000 late-model pickup trucks and SUVs, because transmission oil cooling lines weren't secured properly in their fittings. The same night, GM also announced it would recall 172,000 Chevrolet Cruze compact cars because the right front axle shaft can fracture and separate while being driven.
Al Jazeera and Reuters