9 year old child compulsive liar

[Nellieo]

Our 9 year old child has recently begun lying - not only does he lie, he keeps going with the lie.  He is doing this at school and at home.  We have talked to him over and over about taking responsibilities for his actions.  For example, at school he was caught tapping on a terrarium by his teacher.  He told the teacher that he wasn't tapping.  The teacher explained to him that he saw him doing it.  My son would not own up to his behavior and kept the lie going.  Another example is a situation with a library book.  The children all turned in their library books in the morning.  When they went to the library in the afternoon, he wasn't allowed to check out a book because his wasn't turned in.  He insisted that he had turned it in.  The librarian and his classroom teacher looked on the shelf and behind the desk, it wasn't there.  Again, he insisted he turned it in.  The teacher went back to the room with him where they found the book in his desk.  He still insisted that he turned it in going on to say that someone must have taken his book out of the bin and put it back in his desk.  The teacher questioned him why he thinks someone would have done that.  His only answer was that someone must have done it to get him in trouble.  The other night, he came into our bedroom saying that he saw a man in our house.  He then went on to describe this man's hair color and style, what he was wearing, etc.  My husband walked through our house for over 1/2 hour searching for this man.  Not only was there no man, there was no sign of entry anywhere.  We are at our wit's end - his teacher has suggested a child psychologist which we are considering, but are also concerned that a psychologist might make more out of this behavior than it is.  We are also considering speaking to our pediatrician.  Any suggestions?
Thanks in advance.