This is what I have heard latest :
Rhea was planted in Sushant's life to separate him from Sara, Plan was only to drug him and leave him ruined by declaring him crazy, but while he was in vicinity of people who entered his life due to Rhea , he got to know lot of things related to these rackets. He figured out at end he can't trust Rhea n co and wanted to expose racket ,so he wanted to confide to a friend and he made mistake of telling this friend about exposee he was planning. On June 13th ,They tortured him and brought to his flat where they murdered him.
CBI has gotten all the information n links, they r working silently as sleeper cells since multiple rackets are involved n there is chain of people linked. Plans to divert from this case has been recently foiled by agencies.Preliminary Action can be seen in 2 months. Let's see how true it is in coming months.