Criminal investigation report exacerbates investor concerns, United Health plunges.

The Wall Street Journal reported that the US Department of Justice has begun a criminal investigation into UnitedHealth Group, as the company may have engaged in health insurance fraud. As a result, the company's stock price plummeted nearly 13% on Thursday. Since reaching a historic high in November last year, the market value of this healthcare group has more than halved, exceeding $300 billion. UnitedHealth's stock price dropped to $267 in midday trading, nearing a five-year low. It is currently the worst-performing Dow component stock this year.