You've conveniently omitted the independent third-parties that had seen the data. It's a messy world. Unexpected things happen. How do these third-parties factor in to Occam's razor? You need to add more parameters to your explanation as to why the third-parties would verify the existence of non-existent data.

Here's another possibility: During goes to DePalma to collaborate and asks if DePalma still has the data. DePalma says he doesn't. During sees this an an opportunity to claim credit for the work.

It's impossible to tell which scenario is more likely. Are you really willing to ruin someone's career over purely circumstantial evidence provided by a biased witness?