I view this far differently, I believe that DP was in fact, following a "Good Samaritan" law, helping people who were in danger. Therefore, he should be covered under this law, and not charged for any actions that caused a death or injury.
en.wikipedia.org
"Good Samaritan laws take their name from a parable found in the Bible, attributed to Jesus, commonly referred to as the Parable of the Good Samaritan which is contained in Luke 10:29–37. It recounts the aid given by a traveller from the area known as Samaria to another traveller of a conflicting religious and ethnic background who had been beaten and robbed by bandits.[4]".
In this case, Penny actually saved people from being beaten or robbed by Neely, he was definitely threatening physical harm to passengers. Penny didn't know that Neely was under the influence of drugs, or having a psychotic episode. He truly thought he was being a "Good Samaritan".
Therefore, his actions should be considered within the purview of rescue. Not murder.