Adam Clarke on Matthew 27:38

Two thieves - ΛῃϚαι, robbers, or cutthroats: men who had committed robbery and murder; for it does not appear that persons were crucified for robbery only. Thus was our Lord numbered (his name enrolled, placed as it were in the death warrant) with transgressors, according to the prophetic declaration, Isa 53:12; and the Jews placed him between these two, perhaps to intimate that he was the worst felon of the three.