The engineer is the Captain of his ship, so to speak. He fled while people bled. What kind of animal watches and hears people in agonizing pain and runs. The first article I read about it included a tweet from a democrat senator who asked for prayers and says he was helping people. That should have been the engineer too, but he was more concerned about himself.
The engineer probably fled because he was drunk or high, and wanted to reappear when he would test negative.