I received this info from John Madinger, who an Economic Crimes Adviser for the US Treasury regarding laundering the money.
Anyhow, Cooper. I heard he got 200 grand and they found some of it later, a relatively small amount. Laundering that amount of money wouldn't be very hard. All you need, really, is time, which either got a lot of or none at all. Money launderers face problems with two situations. One is that you have to launder a one-time, large quantity of cash (usually). The other is that you have to launder an ongoing revenue stream. They're different problems with different solutions, but if you've got a lot of time, you can launder a lot of money. $200,000 isn't that much, even back in 1971, even in a one-shot deal. 10,000 $20 bills weigh exactly ten kilos or 22 pounds, and the $20 note is much more commonly used in general circulation than the $100. Further, and this isn't widely known but I wonder if D B might have known it, in 1971, Federal Reserve Banks were routinely tracking $100 notes, at least in large transactions. I don't know how it was done, but they could tell by serial number which bank had sent which bill to the local FRB. This actually tripped up some of the Watergate conspirators. You'll remember that some of the Watergate burglars had cash - $100 bills - on their persons when they were arrested. The FBI traced that money back through the FRB Atlanta branch in Miami to a South Florida bank where it had been deposited by somebody in Nixon's re-election campaign. (Simplifying things a bit, but you get the picture.) Anyhow, the FRBs weren't doing it with $20 bills but one presumes that they had the capability to at least note the serial numbers when they came through because they were doing it with the hundreds in large transactions.
But Cooper's got $200,000 of very, very hot money. How does he use it without having it traced back to him? Here are three possibilities just offhand.
1) He could do it all at once, by essentially fencing it, selling it to someone at a discount. The hot money then becomes someone else's problem and DB walks away with a (considerably smaller) quantity of spendable cash. You'd have to be pretty confident about your fence, however, assured that the person if/when caught wouldn't tell the cops where he'd come by the ransom money. Here's a scenario that might work out well for DB, though not so much for his fence: DB arranges with an associate to sell $200,000 at a substantial discount, say 50 percent. The fence brings the $100,000 to the meet and DB kills him. Then he takes the $200,000 in ransom money out into the forest and seeds it around the place, so if anybody finds it, they'll think he lost it in the jump or died out in the forest. He goes to Maui and lives happily ever after with $100,000 in clean money and none of the ransom notes ever turn up in circulation.
2) DB has an associate who works in a bank. The two of them devise some plan to slide the ransom money into the bank's cash without passing through a teller who might check the serial numbers. The money goes into circulation and can't be traced back to DB or probably even the bank. The problem with this scenario is that eventually, those bills are going to go through another bank or end up at an FRB branch and be detected there. It may take a while, but someday they'll turn up. The advantages are that it would be very difficult to trace back to DB and that he'd probably have more of the $200,000. Maybe he'd only have to pay 15 or 20 percent for the banking service. The disadvantages are that the FBI is inevitably going to catch on and figure out where the stream is. And of course, you've got a live confederate who may be persuaded to talk when the FBI arrives on her door. Still, money launderers love banks, and I'd call this the Scarface Solution because it's how Al Pacino laundered all his coke money in the movie. It's also the one used by Butch Cassidy and the Sundance Kid in real life when they had a problem exactly like DB's. (Incredibly similar, really, even though it was 70 years earlier.)
3) DB just sits on the cash for a long time, the longer the better, and doesn't put any of it in circulation. Ten or maybe even five years later, nobody's looking nearly as hard, and he can just spend it here and there in dribs and drabs, being careful not to do large transactions (over $10,000) that might be reported to the government or that might require him to provide ID. Travel around, spread the money out over a big area and a long time, you could probably go a while without getting caught. Again, though, those bills are eventually going to pop up on the FBI's screen It's my understanding that none ever have.
A really classic example of a very similar situation is Bruno Richard Hauptmann, who New Jersey fried in 1936 for kidnapping the infant son of Charles Lindbergh. Hauptmann got a ransom of $50,000. Not only were the serial numbers recorded (by the Treasury Department's Intelligence Unit, NOT the FBI), but the Treasury people insisted on including some larger denomination gold certificates, knowing that the government was planning to stop issuing those and recall those in circulation when the US went off the gold standard. This made certain parts of the ransom very distinctive and made spending it more difficult. The government circulated a complete list of all of the serial numbers to banks across the country and a couple of years later, a teller picked up on one of the bills that had been used at a gas station. The gas station attendant had written the customer's license number on the note, that led back to Hauptmann, and he was on his way to the electric chair. From what I read, the Cooper ransom notes were all "unmarked" but mostly from a certain FRB and series, and each bill was copied. Although the numbers were later widely circulated, none have ever been found. That wasn't the case with Hauptmann's ransom, however. Bank tellers had been spotting the notes for almost the whole time, and Treasury had been making a map of where the bills had been spent. Most of the locations were in New York City, primarily in the Bronx, and this turned out to be where Hauptmann was living. He was using the money to make lifestyle purchases, spending a $20 ransom note on a $2 purchase and getting $18 in clean money back, for example. Since he had a lot of time and didn't use the money on purchases requiring identification, like buying a car or investing in a brokerage account, or depositing it into his own bank account, he could go on like that almost indefinitely. And over time. the tellers would have gotten less diligent about checking.
So, there are a few of my observations without knowing a whole lot about the case. Personally, I think he didn't make it, which is why none of the bills ever made it into circulation. But I can see at least one scenario (#1 above) that might explain that and have DB surviving and getting to spend at least some money.
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I was hoping to get him on the show, but I’m thankful for this info.