Character Analysis
Vincent is Malcolm's former patient, and he is not a satisfied customer. It's ironic, too, because he confronts Malcolm about his anger on the very evening Malcolm's receiving an award for excellence in helping the children of Philadelphia.
Quel awkward, no?
When Malcolm and his wife go upstairs to celebrate with a little sexy time, they find a nearly naked Vincent hiding in their bathroom. It takes Malcolm a minute or two, but he eventually recognizes Vincent as a former patient.
Malcolm had always thought that Vincent was just traumatized from his parents' divorce, so he never got at the real reasons the boy was struggling. Vincent never really got the help he needed, which is how he's ended up full of rage and anguish in his tighty-whities in his former therapist's bathroom.
Malcolm tries to de-escalate the situation, but Vincent isn't having any of it. He accuses Malcolm of failing him, and as we can see ourselves, Vincent is clearly still very agitated and unstable:
VINCENT: Do you know why you're afraid when you're alone? I do. I do.
It's a terrifying scene. We have no idea what that's about—at least, not yet—but he definitely seems at least paranoid, if not delusional.
Of course, later we learn that, like Cole, Vincent saw ghosts when he was alone, and they were begging for help. Unfortunately, Malcolm never considered that explanation for Vincent's torment, and Vincent never clued him in. Or forgave him.
The end result is a murder-suicide: Vincent kills Malcolm and then himself. The usually ripped and strapping Donnie Wahlberg, who lost a ton of weight to play the role, does a great job making Vincent terrifying but also showing us his own terror and despair.