I am looking for a novel that I read in the late 80's, involving a telepath committing murders.
The book itself was fairly old even then, so was probably written in the 60s, 50s or earlier.
Here is a general breakdown of the plot as I remember it:
The story was set in the U.S. contemporary to when it was written, so early to mid 20th century. There were no sci-fi elements like space-travel, aliens or anything like that.
The main character is gathered into a group by character A and his best friend in order to do a study/investigation into the possible existence of psychic powers. After some exposition they hold a test, similar to a seance, where said supposed psychic powers are expected to make a top spin or pages turn or something similar (I don't remember exactly).
Then character A is murdered, though at first it's believed to be suicide. A repeat of the test reveals that something psychic is happening.
Eventually the main character figures out that character A was murdered by his best friend, who is the telepath. The friend had been "puppeting" character A since they were children to be better - winning at basketball, jumping off a short cliff into a lake, feeling brave in the face of danger, etc...
But character A discovered this when he once tried to do something alone (which he and his friend had done many times) only to fail - revealing that his friend had been psychically boosting him. This is what led to him starting the investigation and eventually causing the friend to dispose of him. I think the "friend" thought of character A as more of a pet than anything.
I'm not entirely sure, but I have a recollection of the main character fighting another puppetted person, jumping on the rails of a roller-coaster, while the murderer sits on a bench below and watches.
Eventually the murderer dies and the main character awakens his own psychic powers.
I think he may also have "assumed control" of the love interest, who the murderer had also been puppeting.
