For nearly 30 years, Die Hard has been considered to be one of the greatest action movies ever made. But even the hardest Die Hard fans have had to wonder about a key moment in the film: the initial encounter between Bruce Willis‘ John McClane and Hans Gruber, as unforgettably played by the late Alan Rickman. Although Gruber quickly adopts a terrible American accent, McClane never seems to be fooled by his act. Which only raises the question: how did McClane know that Gruber was one of the terrorists?

Via Esquire, Die Hard screenwriter Steven E. de Souza has provided an answer to that long-standing mystery. While attending the 30th anniversary screening of The Running Man, de Souza revealed that a key scene was lost that would have made things more clear. “Originally, they get off the truck, the camera craned up, you saw them in a circle and Alan Rickman says, ‘Synchronize your watches,'” recalled de Souza. “They all put their arms out in a circle with the camera moving down and they all had the same Tag Heuer watch. If you notice, the first guy Bruce kills almost by accident going down the steps, he searches the body, looks at the IDs.”

De Souza added that there is a longer cut of the scene where McClane examines the body. “He steals the cigarettes, which is a laugh. He looks at the watch, which gets another laugh because you’re thinking he might steal the watch. As he kills each guy, he notices they all had the same watch…When Bruce offers the cigarette to Alan Rickman, Bruce sees the watch. You see his eyes look at the watch. That’s how he knows that he is one of the terrorists.”

But why was the moment lost? De Souza explained that Gruber’s team was originally going to escape by an ambulance in the garage. When the ambulance escape was cut, the scene where Gruber and his men synchronized their watches was also dropped because it no longer made sense in the film. However, the consequence of that change was that the film no longer explains McClane’s ability to see through Gruber’s lies. Now we know!

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Image: 20th Century Fox