An exhaustive internal investigation of General Motors Co.’s ignition-switch recall shortcomings revealed a “pattern of incompetence and neglect,” but no overarching conspiracy to conceal information from the public, the company said Thursday.

The investigation, led by former U.S. Attorney Anton Valukas, chairman of Jenner & Block, found GM’s handling of the recall was “riddled with failures which led to tragic results for many,” the company’s chief executive office said in a statement.