You can whip the cop when he's confused! They get frustrated by not catching you and enter in a vulnerable state, that's when you can whip them and kill them.
I know what you mean, I've added shadows under characters and a red one under the player to make it a little less confusing, although it helped it still is confusing, and the whip "hook" mechanic is super fast, so that can generate confusion too.
TBH I don't know how to further dial down the confusion meter :P Maybe I have to slow down the action after a successful whip for a second