Are there any major conspiracy theories (JFK, Moon landing, 9/11, etc) that you think might be true?

I have learned that my former company commander from 1963 was investigated as a result of the JFK assassination. He was a primary ballistics expert. I wonder if the investigation could have occurred because the alleged rifle used can't perform as well as stated but one of the same caliber manufactured by anyone a major ballistics expert might have contact with.