Because that of long time he had amazed them with his sorceries (dia to ikanwi cronwi tai magiai exestakenai autou). Causal use of dia with the accusative articular infinitive (perfect active Koin form and transitive, exestakenai). Same verb as in verse Matthew 9 participle existanwn and in verse Matthew 13 imperfect passive existato (cf. also Matthew 2:7 already). Cronwi is associative instrumental and magiai instrumental case.