Best Buy CEO Brian Dunn resigned yesterday amid an ongoing investigation into what the company called his "personal conduct."

A company statement published by Bloomberg states that "certain issues were brought to the board’s attention regarding Mr. Dunn’s personal conduct, unrelated to the company’s operations or financial controls, and an audit committee investigation was initiated." Dunn reportedly left his post before the investigation closed.

The news of the investigation differed from Best Buy's original statement on Dunn's departure, which did not mention the probe.

In its first statement issued Tuesday, Best Buy said there were "no disagreements between Mr. Dunn and the company on any matter relating to operations, financial controls, policies or procedures" and called Dunn's resignation a "mutual agreement."

It later made a second statement by email disclosing the investigation. Director Mike Mikan will serve as interim CEO while a search committee of the board of directors looks for a permanent replacement.

Best Buy is slashing costs and closing stores after it posted heavy losses last month. The big box retailer lost $1.23 billion for its 2012 fiscal year, prompting it to close 50 U.S. retail stores and layoff 400 workers.

The company is shifting focus to smaller Best Buy Mobile stores and plans to open 100 of the new retail locations as it downsizes its larger locations. It expects to have between 600 and 800 of the stores up and running over the next three years, from its current number of about 305.

Like other brick-and-mortar retailers, Best Buy faces stiff competition from online retailers like Amazon. Shoppers are increasingly using their smartphones to check whether they can get a product at a lower price online instead of buying an item in-store.