In the early reporting of the Capital Gazette mass murder, Conor Berry, a reporter for a Massachusetts newspaper, The Republican, tweeted that the shooter had dropped his MAGA hat on the newsroom floor before opening fire. It was a stupid remark, not to mention one for which Berry had no supporting facts, which he has since acknowledged. What makes such tweets particularly toxic is that they color early perceptions of these events, and tend to become urban legends and the stuff of conspiracy theories. BerryÂ’s tweet was similar to earlier instances such as cable talking heads speculating that other shooters...