OT Canon

The answer is not quite as clear as one would like to think. You used the term "orthodox Jews" but that term means many things to many different Jews. Believe me that the word "orthodox" means something totally different to you and me then it does to a Jew and even between Jews it has different meanings. It sometimes depends on which Jew you are asking. Stating that certain books or passages are of God does not mean the same for all who say that. Keep in mind that the Jew does not even understand his own OT scriptures.
One time I was trying to witness to a practicing Jew. She knew her scriptures and practiced them as she was taught. She could even read and write the Hebrew. After speaking to her for a short time I realized that I was not getting through so I asked her a question. "What are you doing for your sin?" I knew she was aware of the OT commands. Here is what she said.
"Well I go to the Rab..i... no...well I..uh... well... UH.." and then she said surprisingly to me and herself. I don't know. Although she was not able to receive the Lord Jesus at that time it was an open door to cause her to think. Just keep in mind that the Jew is asleep at the wheel of their own scriptures so they cannot even understand the old. If they did they would receive the NT scriptures and their Messiah. Here is a link that will give some answers, but like I said much of what goes on with the Jew depends on which one is doing the speaking. And just because someone says that they accept the OT at a certain time does not always mean that is true of all Jews.
http://www.jewfaq.org/torah.htm

 

I guess I was not very clear on what I said, but like I said it depends on which Jew you ask. They did not call it a canon of scripture back then. There is no agreement as to when the Jewish canon came into being. Keep in mind that they did not have a single book like we have today. Much of what they have today took place after the time of Christ. It seems that the Jew has always wrestled with what is in and what is out. Even today different Jews will hold different ideas as to what books to accept as in and out, but they hold a different understandings to what we claim as the 39. Try these links to give a little better understanding. You will need to read at least the first two links to get some understanding.
http://en.wikipedia.org/wiki/Tanakh
http://en.wikipedia.org/wiki/Development_of_the_Jewish_canon
http://users.binary.net/polycarp/apocry.html