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.
The police are still investigating the murder.
The accident was thoroughly investigated.
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.