。
The police have their eye on him.
Literal
Police [topic-は] him [to-に] eye [object-を] are-attaching.
目をつける (めをつける, 'to attach one's eye to' = 'to keep an eye on / to mark') is an idiom used for surveillance, suspicion, or targeting. The progressive ~ている marks the ongoing state of monitoring. The sentence is concise and ominous — a crime-drama staple. In Japanese, 目をつける can also mean 'to take a liking to' in positive contexts, but with 警察 as the subject, the surveillance meaning is unambiguous.