调查取证
diàochá qǔzhèng

“调查” v. inquire/look into; investigate; survey（Source: 《新世纪汉英大词典》）
“取证” v. collect/gather evidence（Source: 《新世纪汉英大词典》）
“调查取证” v. conduct investigation and obtain evidence（Source: 《新世纪汉英大词典》）

新闻例句

调查组的人士表示，待调查取证工作结束后，他们将对相关责任人进行责任追究，并及时向社会公布处理结果。（Source: 新华网）

Officials said they will hold those in charge accountable and promptly release the results after concluding their investigation.