I'm not sure. but I do know that "dying" is not the end of life. and all the deaths are not accidental. all those murders, the people who died though them, it was there time to go. The deceased see their bodies as old, worn out coats they no longer need.
Anyhow, I've been trainning to be a spirit Medium meself. However, there is more then one technique you can use. not all Techiques actually have the mediums' body take the forum of the person they are caller Given, some spirits DO take over a mediums body and talk though it, but most of the time, spirits just send telepathic messages to the medium for he/she to convoy the message to that spirits loved ones.
I've been reading a few books on this subject.