So I decided to go undercover to collect it, "he said."

所以，我就决定当卧底来收集证据了。

youdao

The Statesville officers apparently became suspicious that the drug-dealer was, in fact, an undercover deputy - so they rang the narcotics unit of the sheriff's office to check.

斯塔斯维警探们显然起了疑心，怀疑这名毒贩事实上是卧底，所以他们打电话到警局毒品科查核。

youdao

"A reporter surnamed Zhou said that I need evidence. So I decided to go undercover to collect it," he said.

他表示：“一位姓周的记者说我需要证据。所以，我就决定当卧底来收集证据了。”

youdao

Police there may be reluctant to do so as intelligence operatives rarely own up to undercover operations publicly.

BBC: Anger at 'blown' Mumbai arrests

Doing so en masse could have had an unintended effect of alerting others to an undercover officer's status.

WSJ: Social Media Pose Riddle for CIA