Fetching details from the dictionary...
closing in on (the enemy, first place, etc.); coming close to; pressing hard
pressing hard (e.g. with a question); taking to task; grilling
追跡者が犯人に肉薄している。
The pursuer is closing in on the criminal.
新人選手が優勝候補に肉薄する走りを見せた。
The rookie showed a performance that pressed the favorite closely.
核心に肉薄する取材が高く評価された。
Reporting that closed in on the truth was highly praised.