From what source does congress get its investigative powers? list the five main reasons that committees in congress conduct investigations.

The investigative powers of Congress are attributed to the "all legislative powers" and some also cite the "necessary and proper" clause. The various committees are primarily responsible for the investigations. Investigations are done to gather information, test whether laws are effective or not, inquire about qualifications and or performance or people in other branches, or, on very special occasions, lay foundations for impeachments.