an official attempt to find out the truth about or the causes of something such as a crime, accident, or scientific problem:
The investigation continued for nearly three years.
The authorities are planning to launch a full-scale investigation into the crash.
Baker demanded an investigation of the district attorney's office.
A private detective was hired to conduct the investigation.
the act of investigating something
the investigation of computer fraud
under investigation (=being investigated)
The whole issue is still under investigation.