I think Curtis Hanson . . .

. . . was writing a script for a Don Siegel movie. Whether or not Siegel ever saw it, it reminds me a lot of "Charley Varrick", another perfect crime gone astray, where the hero crook's chief worry is NOT the police.
In the source novel the hero seems motivated by boredom and falls into the robber's hands because he's indifferent to the consequences. Hanson's script is full of the banal details of a life gone off-track, a dull job, and above all, the horror of a modern Christmas as spent by the lonely unattached.
It's no wonder Cullen wants to escape. He knows from the start that Elaine is bogus, but he keeps seeing her--it's better than spending another night alone with the tetras. When he stays and engages with the robber, rather than running like hell, it's as if he's excited by the first real challenge of his life.