BAGHDAD, Iraq - An Iraqi scientist killed in the U.S. invasion and now linked by arms hunter David Kay to possible nuclear weapons research was working on an advanced gun, not atomic bombs, fellow physicists say. They and eyewitnesses also say Khalid Ibrahim Sa'id was killed not when he tried to "run a roadblock," as asserted by Kay, but when a U.S. tank crew blasted his civilian car without warning on an open street. These accounts of the physicist's research and death, provided by 10 Iraqis and supported on key points by U.N. arms inspectors, challenge a core element of...