There was , there is and there will always be institutional manipulation of Bitcoin prices. because bitcoins are in very limited hands. in my opinion Mining pools , exchanges , and big investors are beside bitcoin manipulation.
I agree that the number of Bitcoin holder is limited, we are not taking about large cycle but still I think that the range of manipulation isn't that spread out. People are too much into conspiracy theories and want to beleive that Bitcoin is manipulated more than it actualy could be having in mind the technology that is based on and how the market is functioning.
bitcoiner is only about 1% of the total world population, i think it is a small amount. so manipulation is likely to occur, especially for those who have large capital, so it is easy to drive the price. because we know that price movement is influenced purely from sales volume and purchasing volume