1 : to try to find out the facts about (something, such as a crime or an accident) in order to learn how it happened, who did it, etc.
(+ object)
The police are still investigating the murder.
The accident was thoroughly investigated.
(no object)
The manager promised to investigate when we pointed out an error on our bill.
2 : (+ object) : to try to get information about (someone who may have done something illegal)
He was investigated for his involvement in the incident.