the money trail = when money is being "laundered" for illegal reasons, it is moved from account to account. This is known as money trail. snails leavel a trail of slime that you can follow; money transactions leave a trail of evidence that you can follow.
Please explain these bold words.
Launder- take money, especially cash, from criminal activities and 'clean' it by turning it into legal money in banks
Trail of slime- when a snail moves, it leaves a shiny wet line behind it
Trail of evidence- every time money moves in a transaction, a record is made, so when trying to find criminal money, you can follow the record or movements (in laundering money, it is often moved around a lot)