Say, you own a convenience store for the purposes of laundering the proceeds of a drug enterprise. For the sake of appearance, your store is a real, functioning business that generates a legitimate income.
One day, it all goes wrong: you're arrested and all the money is seized. Assuming you could provide evidence (e.g., CCTV, records of credit card transactions, corroborating testimony) that sufficiently proved a certain sum of that money was made legally, would you be allowed to keep it?