17-year-old son lies about going to a rave
My 17-year old son has a 15-year old female friend with whom he spends a great deal of time. Her mother would not allow her to go to a rave downtown on the weekend, believing she is too young. Her consequence for going would be a lengthy grounding. When at our house, I explained to both my son and his friend that she was not allowed to go, and that I trusted that they would make the right choices. When I spoke with them on a friend's cell phone around 8:00 pm, and they assured me that they were going to a party close by, and were not going to the rave. When they called at 1:00 am, they again said they were at a party close by, were going to stay at a friends house overnight, and had not gone to a rave. They called at 9:30 am the next morning wanting a ride from a local transit terminal.
The friend's mom has found out that they actually did go to the rave, using money given to them by another friend's mom who had been told that it was OK for my son's female friend to go. Neither my son nor his friend had enough money of their own to go downtown, a deliberate move on the part of both myself and her mom. They had been downtown all night, returning around 8:00 am to an in-town transit terminal.
What do I say to my son? His friend's mom has grounded her, and I don't know if they've been speaking with one another yet. He's lied to us about where he's been and other important matters on previous occasions, and always denies, denies, even when faced with what I see as incontravertable evidence. To complicate matters, he has been suffering from depression, and I'm concerned that if I push him on this, he may go the self-harm route in retaliation. I need to say something to him, but what?