jǐng fāng / huái yí / yǒu rén / zài / gēn jiān / yī míng / zhèng rén / biàn / jiā qiáng / le / zhōu biān / de / jiè bèi

警方怀疑有人在跟监一名证人，便加强了周边的戒备。

The police suspected that someone was tailing a witness, so they increased security in the surrounding area.