Spoilers
There are many events that happen in the show that are very big. Here are some of the most important:
- Emily Prentiss was kidnapped and toutured, and after the episode she left to work for Interpol.
- Jennifer Jareau was kidnapped by Al Quaeda members and tourtured, which caused her to miscarriage.
- The head of the BAU, Erin Strauss, was killed by a serial killer called the Trickster while the team was watching. This killer would eventually be caught and killed by the BAU.
- The 2nd ever member of the BAU, Jason Gideon, was killed by a serial killer he never caught. Later on, the team caught the killer and brought him to justice.
Gideon was the 2nd memeber of the BAU. He worked alongside David Rossi for most of his carrer. In Season 9, a killer from Arkansas hunts Gideon down. When he finds, him he kills him with a gun. The team finds this, and they spend the next week finding the killer. They eventually kill him.