Michael Millikin, General Motors Co.’s top lawyer, will retire next year. The general counsel had been criticized after an investigation blamed his department for the company’s slow response to a fatal defect in small cars.

The company will immediately begin an external search for someone to replace Millikin, who will stay through the transition to a successor. The 66-year-old joined the Detroit-based automaker in 1977 and was appointed general counsel in 2009.

GM chief executive officer Mary Barra fired 15 people earlier this year after an internal investigation determined that lawyers and engineers didn’t respond quickly enough to evidence of vehicle defects now linked to 27 deaths. Millikin, who appeared with Barra before a Senate panel in July, approached GM to say he wanted to retire, said a person familiar with the matter.

“There were many who called for him to be let go with the other attorneys who were dismissed and clearly Mary Barra had faith in him and kept him on,” said Michelle Krebs, senior analyst at Autotrader.com. “It’s time for some fresh blood there, for sure. They need fresh eyes in the way they do things.”

Barra has said that GM engineers and lawyers delayed action for more than a decade and failed to report issues to their superiors that may have saved lives if defective ignition switches had been replaced sooner. A report commissioned by GM from former U.S. prosecutor Anton Valukas found that lawyers aware of the fatal defects didn’t act with urgency.

The report also said GM lawyers told employees to avoid using negative words in their communications that might attract legal scrutiny. Millikin and Barra were cleared of wrongdoing in the report.

“Mike has had a tremendous career, spanning more than 40 years, with the vast majority of it at GM,” Barra said Sunday in a statement. “He has led global legal teams through incredibly complex transactions, been a trusted and respected confidant to senior management, and even led the company’s global business response team following the tragedy of 9/11.”

Millikin leaves with unanswered questions about his role in the culture where his people failed to relay important matters and stifled internal communication, said Erik Gordon, a professor at the University of Michigan’s Ross School of Business in Ann Arbor, whose area of interest includes corporate governance.

“Ms. Barra’s effusive praise of him shows that loyalty remains a top attribute of an executive in what she calls ‘new GM,’” he said.

Senator Claire McCaskill, a Democrat from Missouri, said in July that Barra should have fired Millikin. (Bloomberg)