The Los Angeles Police Department conducts a counterterrorism drill in the heart of downtown. Thursday's late-morning demonstration included low-flying police helicopters, officers rappelling from the helicopters and firing of blank ammunition. The scenario involved a response to threats of a weapon of mass destruction. Authorities say the drill was part of the National Homeland Security Association's conference at the Bonaventure Hotel and was being conducted by the Police Department's Counter Terrorism and Special Operations Bureau.