all children lie!!! i really wouldnt read to much into it. tell him that you really dont like lying and that telling a lie about some thing he has done is worse that what he did. when he does tell you the truth go over the top telling him what a lovely boy he is for telling the truth. when he lies to you and you can be sure that he is, simply tell him that you do not like people that lie and by liying to you he has really upset you and say i know you are lying he will soon get the message.
My youngest started lying almost as soon as she could talk.By 2 she was an accomplished liar !! It is part of growing up ...You just have to consistently tell them it's wrong and make sure if they tell the truth they get in less trouble than if they lie. I have 2 other children and they were never convincing liars... but my youngest was. She lies less now. Just give a consistent message that it's wrong and hopefully he will do it less. Praise him when he tells the truth.