A.T. Robertson Commentary John 19:18

"where they crucified him, and with him two others, on either side one, and Jesus in the midst." — John 19:18 (ASV)

They crucified (εσταυρωσαν). The soldiers just as in Ac 22:24f.; the scourging of Paul was to be done by the soldiers.

And Jesus in the midst (μεσον δε τον Ιησουν). Predicate adjective μεσον. A robber (ληιστης, not a thief, κλεπτης) was on each side of Jesus (Matthew 27:38) like Barabbas (John 18:40) and probably members of his band, malefactors (κακουργο) Luke terms them (Luke 23:32).