There is implicit mention of withdrawing from a prior exchange
You cannot get money from exchange A to exchange B without withdrawing it from exchange A
Seeing an amount of monero leave exchange A and roughly *the same* amount arrive at exchange B within minutes, 4 different times, is a classic timing analysis trace
As for "apprehending" him, that is an interesting word choice. They did this to identify their suspect as the money handler so they could pin charges of money laundering on him. It was because of the trace tbat they could identify him as the perpetrator of that crime.
