How too see what my child says on imessage?

When my 16 year old son first got his iphone we mad an agreement that he could not put a lock on his phone unless I knew the password. About a week ago the police called me and said they found my son with a group of teens, they were messing around with drugs so I let him off with a warning (mistake) anyways hes had a lock on his phone since yesterday and he won't tell me the password. How do I look at his Imessages with out him knowing? Hes off on a trip right now for 2 weeks so I have no way of just asking him for his phone. Is there any way on a computer or Iphone to see what he texts using Imessage?

Take away his phone and go to the store you bought the phone from.bring your receipt(or any sort of paper showing you pay for the phone), your id, the credit card you use to pay for the pphone bills.tell them that you want to be able to see what your son is texting other people.

When your son comes back, confiscate the phone until he tells you the password. If he refuses to give you the phone, shut off the phone's service. There's no way to see it unless he shows you, so you should really crack down on him as a parent and make it apparent that he shouldn't disobey you like that.