In Lepage and Brassard's Polygraph, Francois' graffiti says "History is written in blood." It may literally be his response as a student of political science as seen in the beginning of the play, as he discusses the fall of the Third Reich and the condition of Berlin at this point in time.
Francois, the student, explains this comment to David:
It means that we write history through war, fascism and murder.
Literally, this is Francois' political view on history and its connection to violence.
Figuratively, however, if we look to Francois' history, we can see that the spilling of blood has had a horrific effect on his life. In the play, through the use of conversations and flashback, we find that the significant aspects of Francois' life do not deal with a difficult childhood or struggles to be successful in a career endeavor. His life (for the sake of the play—its conflicts and plot development) begins, paradoxically, with the death of his friend Marie-Claude Legare. Francois is the one who discovers Marie's body and calls the police. Naturally, he is suspected of her death; he is questioned and is given a lie detector test. However, the authorities never reveal to Francois that he is no longer a person of interest in the investigation.
The fear and mystique which surrounds the polygraph machine, makes it a useful pressure tactic in obtaining a confession. But such strategies, I believe, should be used only with great care and compassion. Sometimes the psychological response we trigger is so violent as to effect a lasting disorder in the mind of a totally innocent suspect.
Even in explaining this, David never shows compassion toward Francois by telling him the truth. And so, for six years, Francois is haunted and tormented with the perception that he is still believed to be capable not only of rape and murder—but of a friend, at that.
David explains that the authorities do not disclose the results of the test to a subject because they want to see if they can win an unexpected confession when someone still believes he or she is guilty.
...the police never told [Francois] he was released from suspicion...He was never let off the hook.
Though David expresses his concern, we find nothing in the play that convinces us that he cares at all for Francois' wellbeing, or anyone else's:
Poor Francois...they know he is innocent, but he'll probably never be told...it's a strategy to keep everyone in ignorance.
Because Francois has been given no peace, we can only imagine the torment he has experienced—David hears Francois' suffering through the wall of Lucie's apartment:
...he hears violent and lamenting cries from the other side of the wall. The voice belongs to Francois...the cries get louder...
David knows there is suffering in the next apartment; he does nothing. In fact, when Lucie enters, though the cries begin again, he ignores them and distracts her by making love to her.
What little comfort Francois finds is with Lucie. They spend a week together while David is gone. After they make love the last day, Francois leaves, "restless and anxious," still not at peace. Lucie's "To be or not to be" speech foreshadows Francois' state of mind: to live or to die. Marie's blood has become his history—and the only thing that defines him now. At the end...
...without hesitation, [Francois] throws himself in front of the arriving train.
Finally, he has found peace from his "history...written in blood."
Francois is the character who takes the lie detector test. Through an oversight, he is not told the results of his test: did he pass and is believed to be innocent or did he fail and is believed to be guilty? For Francois, the truth is not written in his words nor in the marks of the polygraph test. For Francois, truth is written in the blood that was spilled and is written by the hand that killed or by the hand that investigates. Truth is further complicated because a film is being made of the murder and investigation, thus for Francois, truth can only be found written in the blood of the murder scene.