Он и она минус он и она

The quiet evening of two couples ended. The guests went home. Nothing foreshadowed the tragedy, it would seem. But two of them have their own history and their own secret. They once met and parted, thinking that it would be better for everyone. Did not work out. Three years, neglecting the principles of friendship and family fidelity, they have been changing their legal ...
And now, the next evening, having returned after a meeting each to their home, they find their spouses shot down ... Realizing that the murder suspicion will first fall on them, they flee from the city ...
But the investigation arose an interesting circumstance - the killers left their prints in both apartments ... They drank wine with killed ...
and whose are these prints