... or another Greek translation of the Hebrew. There were 4 to 6 different Greek translations of the Hebrew scriptures extant in the 1st century. The Septuagint (LXX) was allegedly miraculously translated by 70 scholars a couple hundred years B.C., but doesn't really show up in real textual form (like say, the Dead Sea Scrolls) anytime previous to the birth of Jesus... or even prior to the 3rd century A.D., for that matter. There is zero manuscript evidence that Ralf's Septuagint text ever existed at all, since he kind of "back-compiled" it by assuming the NT writers quoted from it, therefore using what appears in the NT and the church fathers' texts under that very assumption.
So what is used today as the "Septuagint" is a contrived compilation that assumes its textual conclusion.
Sorry to bore you with the jaunt into armchair textual criticism.
Oh yeah, the Protestant "Septuagint is a Christian creation" argument form the 19th century nut. dead sea Scrolls show that it is not.
But if you are going to use historical evidence as evidence, I would be careful because then you are placing the entire NYT on the chopping block.
The earliest copies of the complete Bibles (that are in no way in full agreement with the current ones) date back only to the 4th century. The rest of the NT dating to the 2nd century and later are usually pieces of papyrus with half a dozen verse at most, and yet we accept the 4th century Bibles as something handed down by God, index, hard cover, red letters, and all. By your standard, the Bible should be highly suspect. I agree.
That means the NT references to the Septuagint passages are either corrupt Hebrew verses, changed to fit the new Christian theology, or there really was a Greek source which the authors (Pharisee Paul included) of the NT used as reference, in preference to the Hebrew Scripture!
Nevertheless, as things stand right now, the NT references to the OT agree with the Septuagint version, whether real or invented, in over 90% of the cases. So, if it was good enough for the Gospel writers and Paul, it must be good enough for the Church, right?