Final answer:
Judas is identified as the betrayer when he dips his hand in the dish with Jesus, as depicted in the Gospel of Matthew and illustrated in Leonardo da Vinci's 'The Last Supper'.
Step-by-step explanation:
When Jesus announces that one of the Twelve will betray him, the betrayer is identified as the one who dips his hand in the dish with Jesus. This is seen in the Gospel according to Matthew 26, where Jesus addresses the imminent betrayal and pinpoints Judas by this specific action.
Leonardo da Vinci’s The Last Supper uniquely captures this moment by placing Judas on the same side of the table as Christ and the other Apostles, contradicting the traditional opposite-side portrayal. This brings about a sense of psychological tension as the Apostles, and the viewer, try to discern the traitor among them. Symbolically, Judas is also identified as he reaches toward a plate beside Christ and holds a purse, centralizing the narrative and thematic essence of the event.