Unfortunately, Leslie Shay had to die precisely because she was so popular. In an interview with TV Line, Chicago Fire executive producer Matt Olmstead said that the season 3 premiere needed a huge death to shake viewers and the show's characters alike. "Going into it, we knew if we were going to do it, it had to be someone who was going to give us a big impact, as opposed to going for a lesser-known character, which would equate to a pulled punch," Olmstead said about the decision to kill off Leslie. It wasn't immediately clear which character would bite the dust. In fact, Olmstead noted that he and the writers took a long, hard look at every single major character to potentially perish in the trap. However, after considering the pros and cons of each possibility, they ultimately decided to go with Leslie "because it affected the most people."
As for Lauren German, Olmstead said that the the actress took the sad news of her character's impeding death quite well. "There was some discussion that this might be happening, and she was very professional about it. She joked that she wasn't going to miss the Chicago winters."
