To solve that mystery they must be connected with the spirits. Everyone cannot get this experience. Even if someone gets their connection, extracting information from them is not so easy.
A consciousness is a spirit. A human being has many consciousnesses. Spirits are separate elements. (A human being doesn't have a spiritual body.) A human being during his/her lifetime is living with many spirits which have joined one by one since birth. They are knowledge, skills, feelings, emotions, interests and everything. These spirits are not only your consciousnesses but also your memories. Spirits act as your consciousness when you read, talk, write, see, hear and think according to the subjects they have undertaken. Even thoughts are not your own. For example, when you want to take a decision on a subject, one after another the spirits think and you just listen, choose or reject the ideas which they transmit to your mind through your brain in the form of thoughts. Brain is just a media to connect the spirits to your mind. A mind is just a computer's mind. After the destruction of a computer completely you will not get it's mind. The same is the case with the human beings. Soul is nothing but an energy needed for the functionality of a body. It is not a spirit or anything else. After death all spirits which accompanied a person quit and go to different places searching new bodies. No one lives in any form after death. All human beings are just robots made of flesh and bones and toys of the spirits for their games.