捜査【そうさ】
search (esp. in criminal investigations), investigation, inquiry, enquiry
捜索【そうさく】
search (esp. for someone or something missing), manhunt, legally authorized search of a person, building, etc.
捜査官【そうさかん】
(police) investigator
特捜【とくそう】
special investigation
捜索隊【そうさくたい】
search party
聞き込み捜査【ききこみそうさ】
(police) legwork, house-to-house inquiry, canvassing, investigation carried out by questioning neighbours, bystanders, etc.