Captain America: Civil War - 16 Things We Learned From The Directors' Commentary

Helmut Zemo's introduction in Civil War establishes him as a pretty bad guy, but the initial plan would have made a far greater mark, and a far darker one.

The commentary reveals that Zemo would have immediately dialled up the kill number in attempting to get his hands on the key red ledger containing Bucky's trigger words:

"We had an original scene where Zemo was at an auction, a black market auction. And that's how he got his hands on the book, was at this auction. He killed everybody in the auction by gassing the auction. But we just didn't get enough story out of him; it was too mysterious of an opening scene."

Eventually it was decided that the scene simply wasn't clean enough, and the alternative, which tied back to Karpov was used instead. Ultimately, it was the right decision: by the end of the movie, thanks to his motives, you're supposed to sympathise with Zemo, not think of him as an irredeemable monster. Killing an entire auction room full of people would not have helped that.