President Trump hinted this week that something sinister may lurk behind the disappearance or death of 10 government workers tied to sensitive nuclear or space technology, but those close to the various investigations into the disparate cases say they see no links. "I just left a meeting on that subject, so pretty serious stuff," Mr. Trump told reporters Thursday. "Hopefully, coincidence... but some of them were very important people, and we are going to look at it." Social media has recently lit up with theories about the disappearances and deaths, which occurred over three years and involved several researchers and other staff with ties to NASA's Jet Propulsion Laboratory and Los Alamos National Laboratory. Speculation has swirled about whether there's some kind of plot to harm U.S. nuclear or space programs.  But those involved in the various cases have said that what underlies these deaths and disappearances is not a spy-thriller plot, but something more personal and tragic.…