Gil Grissom is the one who eventually apprehends Garland Greene.Think about it, psycho killer running around on the loose in Las Vegas? Who else are you gonna call to bring him down? It helps that CSI and Con Air are both produced by Jerry Bruckheimer.
Gil Grissom got into law enforcement because Cyrus the Virus was his brother.They have the same surname.
Garland Greene is the same character as the gunman, Danny, from Billy Madison.In fact, Steve Buscemi plays the same character in Con Air and all of Adam Sandler's movies, being an increasingly obvious, but increasingly benign, insane man. The movies just aren't released in the proper order. He might also be Mr. Pink and Nucky Thompson, but further research is needed on this, unless the character becomes a Timelord or Highlander-style immortal at some point.