I wouldn't be saying this unless you had asked, but you did, so....
I advise you very strongly against spying on your son's private life in this way. He's not the first teenager to come creeping in at dawn - I certainly did the same thing on many occasions, and so did my children. It doesn't necessarily mean he's 'fallen among thieves', unless you have other evidence of it.
My suggestion would be the same as OTT_Buzzard - talk to your son and explain that to a parent a teenager coming in at that time of the morning can be a worrying thing - he probably doesn't understand that you might be concerned for his welfare. I don't know why we seem to assume that staying out late at night means something bad - you can get up to mischief in broad daylight.
Thank you ladies and gents for taking the time to help me. To those of you who advocate talking to him, believe me we have tried, and to those of you who rightly point out that he wouldn't be the first to come in with the milkman, I agree but the world has become a more unpleasant place and I, when I did it decades ago, had a few bob in my pocket - no mobile, no i-touch, no watch etc. The situation is now also affecting his work in the important GCSE years.
As result of your advice, I will defer this project for a while to see if we can make progress some other way, but MSN is at the heart of this.
I fail to see the why him coming home at 04:35 makes you think he has become a thief. Has anything else happened to suggest that is the case? If not then I think partying / getting drunk / seeing a girl are more likely explanations.
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