{But they shouted} (hoi de epeph(936e)oun). Imperfect active
of epiph(936e)e(935c), to call to. Old verb and a verb pertinent here.
They kept on yelling. {Crucify, crucify} (staurou, staurou).
Present active imperative. Go on with the crucifixion.  Mr 15:13 
has staur(9373)on (first aorist active imperative), do it now and
be done with it. No doubt some shouted one form, some another.