Dr. Warren Weinstein, an American aid worker held hostage by al Qaeda, was accidentally killed in a U.S. counter-terrorism operation, as was an Italian hostage, Giovanni Lo Porto, and another American who was an al Qaeda leader, the White House announced on Thursday. Officials also announced that a separate operation killed Adam Gadahn, another American who became a prominent al Qaeda member. The White House said it was unaware the four were present at the sites. President Obama was set to make a statement after 10 a.m. ET. "The operation targeted an al-Qa'ida-associated compound, where we had no reason to...