A.T. Robertson Commentary Luke 23:21

"but they shouted, saying, Crucify, crucify him." — Luke 23:21 (ASV)

But they shouted (ο δε επεφωνουν). Imperfect active of επιφωνεω, to call to. Old verb and a verb pertinent here. They kept on yelling.

Crucify, crucify (σταυρου, σταυρου). Present active imperative. Go on with the crucifixion. Mr 15:13 has σταυρωσον (first aorist active imperative), do it now and be done with it. No doubt some shouted one form, some another.