Assume that you were responsible for communicating with Denis Grigoryev, what strategy would you implement to get Denis Grigoryev realize the result of his actions?

The most important thing about Denis is that he is completely honest, and that he makes no excuses for his actions. Denis is logical, and he acts logically... but his actions are centered around his needs, and he is unable to see outside the box to understand how his own needs put the lives of others in danger.

In context, Denis is uneducated. He isn't an engineer. Thus, if I were attempting to make him understand the tragedy his actions might result in, I would likely use an example.... a hands on, visual example. A toy train set might serve the purpose and give Denis a visual look at the danger of his actions.