David Hogg (of Parkland, an actual student) and Emma Gonzalez (of New York, a 30-year-old woman who shares the name of an actual Parkland student) have both been falsely accused of being fake crisis actors. [Example]
The Wikipedia article on crisis actors talks about the original use of the term for emergency drills, but explains:
Starting around 2012, the term was appropriated by conspiracy theorists in the United States who falsely claimed that mass shootings were staged, and victims and their families were being played by actors.
This is the use of the term intended here.
Has there ever been a legitimate case of anybody seeking to exaggerate or fake a school shooting or other mass shooting by falsely posing as a victim?