MOSUL, Iraq, May 9 — An American military unit found an abandoned trailer outside a missile testing site in northern Iraq today that they suspect was a mobile biological weapons laboratory. It was the second such find in recent weeks, and could potentially bolster the United States' claim that Saddam Hussein's government was producing biological and chemical weapons. Not long after the division arrived in Mosul in April, Major Handelman said, an engineer from the plant handed over what the major called "a treasure map" of clues to what was buried inside the complex. Mounds of earth, some that looked...