There`s no single manipulator,who is rich and powerfull enough to push the prices down.
There should be a group of big crypto whales and they sell together,forcing the price to go down.When the prices go down,all the small traders start to follow the trend,and eventually the market is manipulated.
Slow and steady decline means small panic.Fast and rapid price crash means big panic.Both scenarios can be created by manipulators.
What do you mean by "artificially bring the prices down to cause panic selling"?

These are my observations so take them with a grain of salt, but I've seen the patterns described below at two markets which are not connected, so there may be some truth in what I think. These are crypto and currency markets, specifically. What I noticed can be summed up as follows.

If you are a manipulator, you are not interested in crushing the price at one stroke. You would rather be interested in a steady decline. First of all, it gives traders time to react and place their orders to buy at what they think low price, that is build support at still relatively high price levels. Second, when you eventually crush this support, you can press prices a little further since there will be less support at lower prices. And third, letting people buy at higher prices will likely make them panic sell at lower prices later, so all-in-all you may achieve better results this way than if you chose to bring the market down in one sweeping blow and then had to face plenty of resistance at lower levels when a lot of support builds up there. The same approach should work perfectly if you are a big whale and want to cash out. It doesn't make sense to dump all your coins at once because that would scare the hell out of everybody and you won't get decent price on your coins.

The bottom line is that if you see prices decline in a steady, intimidating manner with no major rebounds as it happens these days, it is likely someone trying to artificially bring the prices down to cause a panic selloff. Another option is a shrewd whale closing his massive Bitcoin position.