GM_Mary Barra
GM CEO Mary Barra testifies during a House Energy and Commerce hearing on Capitol Hill in Washington on April 1, 2014. Reuters/Kevin Lamarque

General Motors shows an apparent pattern of stonewalling investigations of defects related to fatal crashes, the New York Times reports, citing documents obtained from the National Highway Traffic Safety Administration.

The records cast even more doubt on how honest the biggest U.S. automaker (NYSE:GM) was with regulators over a defective ignition switch that is linked to at least 13 deaths over the last decade.

The company repeatedly found ways not to answer the simple question from regulators of what led to a crash, the Times reports. In at least three fatal crashes, GM said it had not assessed the cause. In another, the company invoked attorney-client privilege as a reason not to reply. And in other cases, it bluntly wrote, “GM opts not to respond.” The responses came even though GM had for years known of sudden power loss in the models involved in the accidents.

The responses are found in documents known as “death inquiries,” which the Times got through the Freedom of Information Act. In those inquiries, regulators ask automakers to explain the circumstances surrounding a crash to help identify potential defects in cars.

On Thursday, GM’s legal department chief, Michael Millikin, is expected to face intense scrutiny at a U.S. Senate hearing. He is scheduled to testify along with CEO Mary Barra, who was grilled before the same panel in April, and other executives.

The Times asked the safety agency for death inquiries on fatal crashes involving older Chevrolet Cobalts and Saturn Ions, which are among the 2.6 million cars with defective ignition switches that GM has recalled since February. Of the 13 deaths linked to the defect, all of which involved Cobalts and Ions, the paper received inquiries for four of them.

When asked about GM’s responses to the government’s inquiries, James Cain, a company spokesman, said Tuesday: “We are confronting our problems openly and directly. We are taking responsibility for what has happened and making significant changes across our company to make sure that it never happens again.”

When asked for comment, David Friedman, the safety agency’s acting administrator, said, “GM’s decision-making, structure, process and corporate culture stood in the way of safety.”