Shares of major U.S. casino operators fell Monday after a gunman shot dead at least 59 people and injured more than 500 in Las Vegas, the largest mass shooting in U.S. history. Shares of MGM Resorts International, which owns Mandalay Bay from where the gunman opened fire, fell to a two-month low, one of the biggest percentage losers on the New York Stock Exchange. Shares finished down $1.82, or 5.56 percent, at $30.77. Wynn Resorts Ltd. shares lost $1.85, or 1.24 percent, closing at $147.07. Las Vegas Sands Corp. shares rose 81 cents, or 1.26 percent, closing at $64.97.