a) Psychopath was a clinical diagnosis in the 1980s, because Brady was diagnosed as one then. That's why he was force fed when he tried to go on hunger strike.
b) Later in his life he was diagnosed as a paranoid schizophrenic with narcissistic personality disorder.
c) The Moors murders happened in the 1960s, not 2017, so the current hip terminology in the DSM prefers isn't relevant. It's what was a clinical diagnosis in 1966.