The blockchain is completely transparant and you could try investigating yourself through a blockchain explorer. There are also rich lists around, and usually the biggest accounts belong to the exchanges. I think if you search on google you may find some people who did prior research: I've come across addresses which people claim belong to Bittrex, Binance or Coinbase. Once you have those you can simply see every transaction made to, and from it. Also in a historic sense, so you could theoretically investigate the exact period you're describing. In reality I imagine that so many transactions make it into and out of Coinbase at any given time, that it'd be like sifting through a haystack