Hey Shin.
I am avoiding the dictionary with this response.
When you cooperate with someone, you are helping them with something that they are doing. The project usually belongs to the other person and you contribute your knowledge or skills to its success.
When you collaborate with someone, you are more of an equal partner, the project belongs to both of you, it is a labor taken on by more than one person towards a common end.
"He was very cooperative in my investigation" = He helped me with MY investigation.
"He collaborated in the investigation" = There was an investigation carried out by more than one person.
peace,
Mr Spears.