There is an interesting debate as to whether the quotations of the Old Testament in the New Testament are from the Greek Translation of the Old Testament, the Septuagaint or whether the copies we have of the Septuagaint have been altered to fit with the New Testament quotations. John Owen and Francis Turretin did not believe that the apostles were quoting from the Septuagaint. There is a good introduction to this debate
here. A fuller analysis is found
here. Other contributions are
here and
here. There is no complete agreement on the fact that Greek translation of the Old Testament existed and was widely used at the time of Christ.