KISS THE BLOOD OFF MY HANDS: what's the magic word?

What intrigued me most about this 1948 film was its lurid title. How exactly would they work it into the story? Would it be a plaintiff plea to a loved one by someone looking for comfort in his darkest hour, or a command, barked pitilessly by the victor to his groveling defeated enemy? And what would the circumstances be that would give rise to such an unusual utterance?
Sadly all of these questions and more were left unanswered by this drama which wants to be a film noir but doesn't quite have the nerve to pull it off.

Burt Lancaster stars as Bill Saunders, a mentally disturbed ex-soldier on the run in postwar London who finds an unlikely friend and lover in Jane Wharton (Joan Fontaine), a lonely nurse, whose flat he takes refuge in after accidentally killing a man in a pub brawl.Despite the unconventional nature of their introduction Jane finds herself drawn to this troubled, tough but tender man who wants to do the right thing but just can't control his temper.
If director Norman Foster had remained true to his film noir aspirations this love story would have ended very differently to the way that it does, which is a shameful cop out that betrays almost everything that's gone before. Up to that point he'd done well to adapt the conventions of a uniquely American cinematic genre to a British setting, creating a sense of doom that while never scaling the heights of 'Double Indemnity' or 'The Big Sleep' does ok in the circumstances.
Lancaster is testosterone on legs. Virile is barely adequate to describe his presence on screen and it's not difficult to understand why Jane would be irresistibly drawn to this bad boy despite all the warning signs (starting with his confession that he's just killed someone). Fontaine is surprisingly likeable and appealing and - most importantly - convincing in a part that she's really a few years too old for.
Third billed Robert Newton, however, is another matter. His literally eye-rolling performance as the blackmailer who delights in tormenting the already tormented Saunders is a thick slice of boiled ham. His most famous film role, as Long John Silver in 'Treasure Island' was still 18 months in the future but he appears to be warming up for it here, with a parody of a cockney crook that even Dick van Dyke would blush at.
It all adds up to a routine drama that could have been so much more.