It isn't that hard to figure that out even if you don't have actual evidence. Logically, if you have enough coins to manipulate the market to your advatage, why won't you? And i think there have been several instances where a single transaction from the same wallet address bought or sold enough coins to move the market.
You got it right dude,theres no concrete evidence about that manipulation from the whales,but logically i guess it is,since they can do everything because of large amount of bitcoin they have and may use it as andvantage,and as i believe the same reason thats why US government are now into this issue to investigate about manilulating