Shares of the electric carmaker tumbled as much as 10 percent on Friday, with investors on edge after a tumultuous August during which Musk proposed and then abruptly pulled the plug on a go-private deal. Chief Accounting Officer Dave Morton resigned because of discomfort with the attention on the company and pace of work during that time, Tesla said in a filing on Friday. Morton, whose departure comes after the U.S. Securities and Exchange Commission opened an inquiry into Musk’s aborted plan, joins a list of executives who have left Tesla recently.