General Motors CEO Mary Barra has confirmed that 15 employees have been fired over the company's recent ignition switch recalls.

The automaker has also determined that no senior executives were to blame for a delayed vehicle recall involving defective ignition switches linked to at least 13 deaths.

Barra made the announcement as she released an internal investigation into the recall of 2.6 million older small cars for defective ignition switches.

The report by the Detroit automaker on its internal probe also concludes that there was no concerted cover-up of the faulty parts, according to Reuters. Instead, the company points to cultural failings at the company, according to Reuters, citing a source familiar with the contents.

Barra called the internal investigation "brutally tough and deeply troubling."

It took GM over a decade to report the switch failures to its customers.

The probe also found that GM's general counsel, Michael Millikin, was not responsible for the mishandling of defects and the recall delay, the source said.

Millikin, who led the internal probe with former U.S. prosecutor Anton Valukas, is not expected to be let go by the automaker.

Not everyone is happy that no higher ups within the company will be punished.

"How do you truly fix a culture of carelessness and cover-up without cutting the head off the snake?" said Robert Hilliard, a lawyer for a plaintiff in a lawsuit against GM related to the ignition switch defect, according to Reuters.

Switch designer Raymond DeGiorgio is expected to be one of the employees let go, according to the source.

The findings, first reported by the Wall-Street Journal, are expected to be made public later on today, June 5. 

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