Investigators have a favourite move. Find an account that looks wrong, then walk the money backwards. Who paid in? Who paid them? Who paid them before that? Do it patiently and a laundering scheme comes apart one transfer at a time.
It’s called backward tracing, and across most of the financial system it works beautifully, because most of the financial system writes everything down. A bank transfer carries the sender’s name. A payment message records who paid whom. The trail is there because the plumbing was built to leave one.
Not all of it was.
When Money Mixes
Start with the simplest case. An account holds 100 from one source and 100 from another. The owner then pays someone 100. Which 100 did that person receive? Nothing can answer that. Money carries no label, and once two sources sit together in one account, a payment out can’t be matched back to either.
Now look at it from the receiving end. The person paid sees 100 arrive. They can’t see what else was in the account, so they have no way to know where their payment came from. If one of those sources is later questioned, they still can’t tell whether any of their 100 had anything to do with it. Neither can anyone else.
That is the whole problem, and here it involves one payment and two sources.
Alt text: Illustration of funds from two sources mixing in one account, showing why tracing rules matter
The Account Built Not to Remember
Now multiply that problem by a few hundred transactions a day.
Across much of Southeast Asia, cross-border currency exchange runs through pooled settlement. A regulated operator keeps one clearing account. Unrelated customers pay in, unrelated recipients get paid out, and nobody is credited from a particular sender. They’re credited from the pool. Industry estimates put the share of cross-border money entering Thailand from its neighbours that moves this way at somewhere between 40 and 55 percent, a model FXStreet has explained in detail.
Here’s the part that matters. In a pool, the link between any one deposit and any one payment out was never recorded. It isn’t hidden or encrypted. It was simply never made, and that is the whole point of a pool. It’s why the system settles faster and cheaper than a bank wire.
A backward trace that runs into a pool has two options. It can apply a tracing rule to thousands of interleaved transactions and produce an answer built mostly on assumption. Or it can treat any contact with a suspect deposit as contamination, in which case everyone who used the pool that day is contaminated. The second option is easier. It’s also close to useless as evidence, because it can’t tell the guilty from the merely present.
Brokers have noticed. The Thaiger reports that backward-tracing enforcement is turning into a counterparty risk problem for currency exchange brokers, who now have to wonder what else passed through the accounts they settle against.
The rules were written with this in mind. Under Thai and international frameworks, due diligence in pooled settlement sits with the regulated operator, the only party that can see who is paying in. The Financial Action Task Force’s Recommendation 3 makes intent or knowledge an essential element of a money laundering offence, and a pool can supply neither. What happens when enforcement shifts the liability onto recipients anyway is something FinTech News Singapore has looked at closely.
Thailand’s Test Case
Thailand’s Anti-Money Laundering Office (AMLO) has frozen more than 20 billion baht, equivalent to more than USD 600 million, in assets connected to Cambodian businessman Yim Leak and his wife. It is the largest asset freeze in the country’s history. AMLO has stated that it has identified links to criminal activity. No criminal charges have been filed. That is a freeze-to-transaction ratio of approximately 4,000 to 1.
According to his legal team at Dentons Pisut and Partners, one of the largest international law firms, the transaction at the origin of the case was a currency exchange transfer worth approximately USD 150,000, processed through a regulated operator’s pooled clearing account, with no visibility into the upstream origins of the pooled funds. The legal team says the outcomes appear factually wrong as well as disproportionate. It also points to a 2024 AMLO investigation that reviewed substantially the same assets connected to the same party, found no connection to criminal activity, and returned them.
The legal team’s argument is the pool problem, applied. A credit out of a shared account isn’t a traceable payment from any particular depositor, and treating it as one asks the method to prove something it can’t. That 4,000 to 1 ratio is what the gap looks like at scale, as reporting on cryptonews.net has set out.
What the Courts Have Said So Far
Thailand’s own judges have been here before. In one comparable case, the Bangkok Criminal Court acquitted every defendant after finding that sharing an regulated currency exchange and overlapping pooled accounts didn’t prove the business clients were part of a criminal organisation. In 2025, the Chonburi Provincial Court went less far but in the same direction, finding real limits to conclusions drawn from pooled-account flows alone.
The forfeiture now sits with the Civil Court, which is a different arena. The case runs against the property, not the person. The bar is lower, and the owner carries much of the burden. Whether the criminal courts’ logic survives the move is the question the case turns on.
Where the Method Still Belongs
Backward tracing doesn’t need retiring. Like any financial channel, a pooled account can be misused, and following money into one is a reasonable way for an investigation to begin. The real question is how much weight the trace can carry once it gets there.
As a lead, quite a lot. A pooled-account trace can tell investigators where to look. On its own, though, it can’t show that any particular recipient knew anything, and that is exactly what the law asks for. The Civil Court will weigh the evidence on both sides, none of which has yet been tested in public.
“Follow the money” remains the right instinct. Thailand’s Civil Court is about to decide what it’s worth when the money was never labelled in the first place.
