jīng / guò / míng / chá / àn / fǎng / ， / jǐng / fāng / zhōng / yú / zhǎng / wò / le / fàn / zuì / xiàn / suǒ / 。

经过明察暗访，警方终于掌握了犯罪线索。

Through careful observation and secret investigation, the police finally obtained clues about the crime.