Citing an anonymous source, WSJ said Wednesday that the board members never received internal reports on faulty ignition switches in some of the company’s smaller car models, including the Chevrolet Cobalt and the Saturn Ion. Documents have shown the defect, which was responsible for 13 deaths, was identified by GM engineers in 2005, but the automaker did not order a recall of the affected vehicles until February.

The Detroit News reported that the board has hired attorneys at the firm Wachtell, Lipton, Rosen & Katz to lead the internal investigation. GM CEO Mary Barra previously hired Jenner & Block chairman Anton Valukas, a former U.S. Attorney, to investigate the company’s handling of the vehicle defects.

A GM spokesman declined to comment on the board’s activities. A Wachtell spokeswoman did not respond to Fortune‘s request for comment.

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The board is hoping to learn how information about the defect was shared within GM, and why it never came to the board’s attention. The finding are intended to help the company better navigate any future safety issues with its vehicles.

The internal investigation is expected to wrap up in either late May or early June. Barra plans to hold off on releasing an in-depth public response to questions about the recall until the probe is finished, WSJ reported.

GM CEO Mary Barra apologized for the deaths recently when she testified in front of Congress about the botched recall. Earlier this week, the family of a woman killed in a 2007 crash involving a Cobalt with a faulty ignition switch asked to have a lawsuit against GM it settled last year reopened. The family, which did not disclose the terms of their initial settlement, now accuses GM of attempting to cover up the company’s previous knowledge of defect.