[Post significantly edited/updated, updated and updated again on Sunday].
I am not pretending to offer a diagnosis here, but I do ask a few diagnostic questions in this post. There is much we don't know, but what we do know gives rise to certain questions for the psychologically minded to ponder.
James Holmes, the Aurora, Colorado mass murderer identified himself to the police as The Joker. Now when you ask someone who he is and he answers you, you might learn something about him by listening to his answer. When he says: "I'm The Joker," he's telling you an important part of the story in his head, which isn't your story or mine; it's his story about who he is and what he's done. If you hope to understand his mind, then you must try to hear his story.
So who is the Joker and what is his story?
The Joker is sometimes portrayed as having a fourth wall awareness.
[T]he imaginary "wall" at the front of the stage in a traditional three-walled box set in a proscenium theatre, through which the audience sees the action in the world of the play. The idea of the fourth wall was made explicit by philosopher and critic Denis Diderot and spread in nineteenth-century theatre with the advent of theatrical realism, which extended the idea to the imaginary boundary between any fictional work and its audience.
In his own mind, was Holmes crossing The Fourth Wall? Many survivors said that they weren't sure if the attack was real or part of the show or just the antics of an enthusiastic audience member.
The Joker [...] has been consistently portrayed as capable of hijacking broadcasts.
Is hijacking a movie like hijacking a broadcast?
The Joker has been portrayed as highly intelligent and skilled in the fields of chemistry and engineering, as well an expert with explosives. [...] The Joker's versatility in combat is due in part to his own extensive array of hidden gadgets and weapons on his person that he often pulls out on a moment's whim, rolling a handful of explosive marbles on the ground [...]
Not only did Holmes begin his attack by setting off explosive gas canisters, but Holmes booby-trapped his apartment with explosives.
[The Joker] has no true personality of his own, that on any given day he can be a harmless clown or a vicious killer, depending on which would benefit him the most.
Did Holmes similarly experience identity confusion, including, perhaps, confusion over whether he was a harmless person or an evil killer? (This possibility could take us into a lengthy discussion of a psychological defense known as splitting and the related problem of identity confusion. These related phenomena, if they are present, are characteristic of certain personality types (example) as well as a borderline-level personality organization, which, I must caution, is not one and the same with the DSM version of BPD. Follow the links if you'd like a bit more information.)
More on The Joker's story:
[The Joker] himself is confused as to what actually happened [regarding the trauma that disfigured him]; as he says in The Killing Joke, "Sometimes I remember it one way, sometimes another... if I'm going to have a past, I prefer it to be multiple choice! Ha ha ha!" In Arkham Asylum: A Serious House on Serious Earth, written by Grant Morrison, it is said that the Joker may not be insane, but has some sort of "super-sanity" in which he re-creates himself each day to cope with the chaotic flow of modern urban life.
The Joker isn't sure how he became so damaged, and he's at sea in a world that he's finding difficult to navigate. Could this tell us anything about how Mr. Holmes sees himself and how feels about his position in the world? Does he adapt by re-creating himself as a different character when he can't handle the challenges his world presents?
Grant Morrison wonders if it's "urban life" rather than insanity that's at issue for The Joker, but the relevant questions for any particular individual are: what kind of [adaptive] coping capacities and defenses does this person bring to the challenges he faces in his particular world, and what are the implications of reliance on his particular adaptive style? Do his available adaptive capacities help him to overcome challenges and thrive? Does he limp along? Does he collapse at some point? Overall, are his adaptive efforts more generative or destructive?
Implicitly, the character of The Joker is a symptomatic adaptation to the world by a brilliant man filled with rage, possibly over an incident that disfigured him and made him an outcast. Like most symptoms, The Joker is an attempted solution to a problem. The Joker is a way to manage the disappointed, impotent rage of great promise tragically destroyed. No matter how angry he gets, The Joker can't undo the loss underlying his sense of alienation from the world. But as The Joker, his brilliance will be seen by those who would otherwise ignore him, or worse, avert their eyes. The Joker responds: "you will look at me! I will interrupt your newscast, your movie, your life. I will be seen and I will avenge my loss. I will make my tragedy your tragedy."
Question: "Who am I and what should I do about this world I can't manage?"
Answer: "I am The Joker and I will handle it the way The Joker does."
Of James Holmes and the question: why now?
One reason we often see psychological problems become acute as young people are leaving the nest is that structures, supports and interventions provided by parents and schools continue to drop away in college and, subsequently, as the time nears to enter a world that increasingly calls upon one's own adaptive capacities to meet the challenges of life.