Tesla CEO Elon Musk and his brother are under investigation by the Securities and Exchange Commission for possibly violating insider trading rules, according to media reports. The Wall Street Journal, citing unnamed people familiar with the probe, said the investor watchdog agency is looking into sales of Tesla shares by Kimbal Musk, a member of the Tesla board, just before his brother, Elon, announced on Twitter that he would sell 10% of his own Tesla holdings, a move that sent Tesla (TSLA) shares sharply lower in the days that followed.