How I Unraveled a BDT 15 Million Circular Chain in Nagad Wallets in 7 Steps
AI-generated illustration High‑Stakes Hook It was 02:13 AM on a rainy Tuesday. My dashboard flashed a red line: BDT 15 million moved through five Nagad accounts and landed back where it started, all within 27 minutes. The BFIU had just sent a notice that any circular flow above BDT 100,000 triggers a mandatory SAR. My phone buzzed. The audit team was breathing down my neck. I had 30 minutes to prove whether this was a harmless peer‑to‑peer shuffle or a sophisticated layering attempt. The Hidden Problem Most AML rules in Bangladesh treat each transaction in isolation. We flag large amounts, rapid velocity, or known high‑risk counterparties. But a circular chain disguises itself as a series of legitimate transfers. The standard rule‑engine missed it because every hop was below the BDT 100,000 threshold and involved “verified” customers. The real issue? Our graph‑based alert only looked two hops deep. Anything deeper slipped through. Technical Breakdown & Logic Flow First I asked: Wh...