I want to add to these answers, the concern I have over "someone I know". How well do you know them? If the police or organised crime/FBI style of law enforcement knock on your door, or get involved, you will go a long way to clear yourself of other than claiming personal naivety, if you can identify the "someone". The concern I have is that I don't know, from your question, if you can do so.
Your problem is that there is no trace where the money came from, where it went, or who has it now. A reasonable assumption would be that you signed everything, so an associate of yours has ended up holding it. So suspicion is likely, and your defense will have a high chance of sounding flimsy.
It's a bit underhand but as there seems a very high chance 1) there is serious criminal activity going on, 2) you're being used as a fall guy and set up by this "someone" in it, I would be a bit willing to do the following:
- Get the guy's fingerprints on something. A phone you offer them to look at a picture, a glass, a can of soda, whatever it is that you can give him as part of ordinary conversation, that he would take without thinking, then give back or put down, and you can hold without rubbing the new prints.
- Get a photo at some time. If it's a criminal matter, you can bet that the moment there's a wisp of any issue, or he pulls out (and you might not know when it happens), he might never be seen again. All you'll have is a story about "someone". A photo will be very useful in worst cases, if you can take one without being seen.
Then, if you contact the police or they knock on your door, or accuse you/hint they think you were a knowing party, you have something concrete to give beyond a vague description.
At which point, now contact a lawyer, who may well then say to go to the police. A lawyer may well be important to ensure you minimise the risk of issues when you do so.