Existentialism

"I like “Milk,” which has a strong, showy, often moving performance from Sean Penn as Milk and one gorgeously directed and choreographed sequence — shot by the great cinematographer Harris Savides — in which Josh Brolin, oiled in flop sweat and hair grease as Milk’s killer, Dan White, walks alone through a series of grim institutional corridors that put the killer’s existential isolation and desperate journey into bold visual terms." - Manohla Dargis, In the Big Picture, Big-Screen Hopes, December 18, 2008.

What does 'existential' mean in that sentence?