Your son needs to consult in private with a criminal defense attorney, immediately. He must not discuss this matter with anyone else until he does. That includes discussing it on the internet, and it especially includes talking to the police. DO NOT TALK TO THE POLICE. If they try to talk to him, he must say "I'm sorry, but I don't want to answer any questions or consent to any searches, and I'd like to speak to a lawyer, please." Or, if you want to be technical, say "I'm invoking my right to remain silent and my right to counsel." Say that, ONLY that, then DON'T SAY ANYTHING ELSE.
Talking to the police without your own lawyer present can never, ever help you. The police are allowed to lie to you and trick you to get you to make self-incriminating statements. They can misrepresent what evidence they have. Or they will say, look, I'm sure this is all a misunderstanding, why don't you tell me your side of it - and then you'll say something they can use against you, and lose any chance of a defense. Do not fall for it. Do not talk to the police. Ask for a lawyer. Shut your pie-hole. Have I made myself clear?
Why do you need a lawyer? Only a lawyer can hold the police accountable for statements they may make to you about what evidence they have, or don't have. If you say one thing about a conversation, and a police officer says another, who do you think the court is going to believe? The police officer who's been on the force for ten years, or someone who's accused of being a criminal? People always believe officers above ordinary citizens (even though officers lie fairly commonly), if only because officers tend to be more coherent and articulate in their presentation. Only a lawyer can be sure of getting access to evidence the police hold that might help you. And only a lawyer can tell you what it's safe to say, and when you need to keep your gob shut (answer: most of the time; but it's impossible to give specifics without being there).
You have the right to be appointed a lawyer, at taxpayer expense, if you're charged with a crime. So, no excuses. This is not a problem that can be solved with a few words over the internet.