Traditor autem (But the traitor) is the sixth and last antiphon of Lauds on Maundy Thursday.
The antiphon comes from Mark 14:44, and is followed by the Canticle of Zachary (Luke 1).
Dom Guéranger explains:“The Church now intones the sweet canticle of Zachary, which she repeats every morning. Its joyous accents strangely contrast with the sadness caused in us by the Passion of our Jesus, the Sun of justice. It was during these very days, that the remission of sins was wrought through the bowels of the mercy of our God; but the divine Orient rises not upon us from on high and in His splendor; He is about to set on Calvary by the most cruel of deaths. Let us weep for ourselves, while we weep for Him; but let us look forward to His Resurrection, which is to be ours also” (1)