A.T. Robertson Commentary Luke 6:16

"and Judas [the son] of James, and Judas Iscariot, who became a traitor;" — Luke 6:16 (ASV)

Which was the traitor (ος εγενετο προδοτης). Who became traitor, more exactly, εγενετο, not ην. He gave no signs of treachery when chosen.