Every time police break a case, they only have to patiently follow the threads and often they will come upon another organization. These instances of "a case within a case" account for a large proportion of police successes.
每次破獲一個案件後，只要耐心抽絲剝繭，往往會追到另一個集團，這種「案中查案」方式，佔了破獲案件的很大比例。