Investigative describes work whose job is to investigate: to dig, ask, and check until you find out what is true. Investigative journalism is reporting that hunts for hidden facts, not just repeating a press release. Police may have an investigative team on a crime. A scientist can do investigative work too, though people more often say research. It is an adjective. The person is an investigator; the act is an investigation; this word tells you what kind of work it is. It sounds serious and a little formal, which fits: this is not casual looking-around.