Of course, the problem with most crimes is not trying to find out whodunnit. It’s trying to get enough proof to convict beyond reasonable doubt.
I’m sure the local cops and the DEA have a pretty good idea who’s the drug pyramid in any location. It’s likely the odd freelancers and exact details of shipments (in time to intercept) that eludes them.
So, just because you tell the IRS “I made $500,000” does not mean you provide enough detail for a conviction. Lots of people brag about stuff they never did - ask any high school boy or girl.
So if you don’t have detailed documentation - except maybe bank deposit records - what can they nail you on? If they were to come back and say “we think you owe more” they would have to produce some sort of proof. I wonder if “you musta took 10% for spending money” would fly? Maybe, if there were no withdrawals for beer and groceries and spending money along with your deposits. The moral being, don’t lie.
You can always use the “I don’t remember the details”, and the worst they can do is calculate that you owe more money. That calculation has to be reasonable thogh. They can’t just say “We think you made twice as much” they ahve to back it up with something, such as a net worth evaluation. “You delcared $500K but we see 6 new Labourghinis in the driveway”.
Do you have to tell them what it was from? They’re not stupid, they know it was something interesting. What they may nail you on is failure to keep receipts, stuff like did you keep documentation so they can go after your suppliers or customers? Not sure if that is anything the IRS itself cares about. I know in Canada, if you have employees and don’t keep the necessary witholding taxes off of their pay, and provide the details monthly to the tax department, they will nail your cheeks to the wall.
So they pass the info to the DEA… Well, if you’re making half a million a year for a while, don’t you think the DEA already knows who you are? They just haven’t had a chance to catch you red-handed yet.
The real question is the proceeds of crime - you are laundering money. Is money laundering a crime in itself, or is the fact you don’t declare it as income the real crime.
I recall about 20 years ago an article about over-zealous stereotypical law enforcement in northern Florida who had pushed the limits of DWB, “Driving While Black” to a new extreme of highway robbery. They would pull over anyone who “didn’t fit”, i.e. wrong colour to be driving that car. If the person had too much cash on them - say, $3,000 or $10,000 and could not explain where it came from (to the satisfaction of the officer), it was confiscated. One guy said he has sold his stuff and was moving back to Atlanta. The police told him he could have his money back if he fought the “possession of proceeds of crime” in court; if the guy was telling the truth, how was he going to afford a lawyer?
Ah, America.