**Spoiler warning: Don’t read any further if you plan on watchin John Cusack’s ‘Identity’. **
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The whole movie was just about what went inside Malcolm Rivers’ (the bald guy’s) head. He saw his mother murdered before his very eyes as a little child and that traumatized him and left scars that never healed.
None of the victims (that are shown: Cusack, Ray Liotta etc.) existed in real life; although there were 9 people murdered in a motel in Nevada that night.
The characters shown were basically different identities Rivers had developed in his mind. Multiple Personality Syndrome essentially. The rage got to an unbearable point at one stage, and Malcolm Rivers ends up murdering 9 strangers physcially, when he is really eliminating 9 identities he knows in his head mentally. The ones who’s charactersitics he assumes and that have distrubed him since childhood.
Remember the part when all the characters find out all their birthdays are May 10th, that’s because they are the one and the same: Malcolm Rivers. He has also concoted their names; the part where he (in John Cusack’s “role”) realises all the people present in the motel that night have surnames ending with those of U.S States (Larry Washington, Mr. Rhodes, Paris Nevada etc.)
It is the little boy who eventually kills all the other identities in his head, as it is his way of coping with his crisis by eliminating all the various “personalities” he had developed. The pity was that real people had to die in order for him to find complete peace.
That included killing the Doctor who saved him in the end (the 10th person), when all he thought he was doing in his sub-conscience, was killing Amanda Peet’s “personality” in his mind.