From YOUCAT, fact 105:
105: How did the disciples come to believe that Jesus is risen?
The disciples, who before had lost all hope, came to believe in Jesus’ Resurrection because they saw him in a different way after his death, spoke with him, and experienced him as being alive. [640-644, 656]
The Easter events that took place in Jerusalem in the year 30 are not a made-up story. Following the death of Jesus and the defeat of their whole cause, the disciples feld (“We had hoped that he was the one to redeem Israel,” Lk 24:21) or else barricaded themselves behind locked doors. Only their encounter with the risen Christ freed them from their paralysis and filled them with an enthusiastic faith in Jesus Christ, the Lord of life and death.