Investigators examined burnt wreckage and interviewed survivors Tuesday in South Korea in an effort to figure out why a U.S. military helicopter crashed, killing 19 Marines and injuring 16. Monday's crash was the second fatal U.S. helicopter crash in South Korea in four days. Both choppers were participating in the annual "Team Spirit" military exercises, which include about 200,000 U.S. and South Korean troops. On Monday, a Sikorsky CH53-D Sea Stallion helicopter crashed in a mountainous region near the southeastern port of Pohang. A Marine Corps spokesman said the injured included a Marine on the ground.