They could have been the culmination of a plan over a long period of time. If he was indeed unbalanced, had a personality disorder or depressed then this starts him off in a bad place. I do not know what medications he was prescribed, but I have had some that made me worse rather than better. Anti-psychotics or anti-depressants have an eye-watering amount of warnings in the literature of side effects. In my darkest hours I planned my own demise quite thoroughly. It is possible that he worked on this in his head and once he locked the door behind the Captain, there was no going back.
Psycho is a unhelpful word, as its open to interpretation to what it means.
yes your right what should i change it to?? is sociopath more correct