Congressional investigators on Thursday began poring over former U.S. Attorney Anton Valukas’ 300-plus-page report on the events that led to General Motors’ recall of 2.6 million cars, and House and Senate officials said GM officials will be called back for more hearings on Capitol Hill.

House Energy and Commerce Committee Chairman Fred Upton, R-Mich., said he spoke to GM CEO Mary Barra on Thursday morning before she went before a town hall-style meeting in Detroit to discuss Valukas’ report with employees. He said it will take time to scrutinize the report but considered the initial findings “deeply disturbing, suggesting that communications and management failures ran deep” at GM.

Upton said committee leaders will hold a hearing in the coming weeks to discuss Valukas’ findings and expect both Valukas and Barra to appear. In April, she appeared before the Oversight and Investigations Subcommittee, which is part of Upton’s panel, as well as a Senate consumer protection subcommittee.

GM has delivered more than 1 million pages of documents to the House investigators, who, like their counterparts in the Senate, want to know why it took so long to order a recall with warning signs going back more than a decade that Chevrolet Cobalts, Saturn Ions and similar vehicles had defective ignition switches.

Congressional investigators also want to know why regulators at the National Highway Traffic Safety Administration didn’t act sooner to force GM to order a recall. NHTSA Administrator David Friedman said in April that formal investigations were considered in 2007 and again in 2010 but that the evidence did not appear to warrant it.

Friedman - whose agency has already levied a record $35 million fine against GM for not ordering the recall sooner - has said NHTSA would have reacted differently if it had known, as at least some at GM did, of reports linking air bag nondeployment to the recalled vehicles. GM ordered the recall beginning in February.