Citadel is a market maker, they may be long or short securities in the course of business and not a "shareholder" in the same sense as an investor.
This is an old article and ever since $AVXL started trading options the trading around option expiration got "wonky" (my technical term). Put this in your conspiracy pipe and smoke it. Enjoy.
Citadel is one of the Market Makers...behind all the manipulation....you should read their balance sheet to see how much shorting they are responsible for....Their goal is to bankrupt biotechs...Just think about this...If they bankrupt a biotech they NEVER have to close their short position nor their naked short position nor do they have to report profits. Thats because they don't need to close out their shorts...company is bankrupt and thus they is nothing to buy....the liability of "shares sold and not yet purchased" stays on the balance indefinitely...it just grows and grows and grows as does their cash balances...take a look at citadels's liability of "shares sold and not yet purchased"...it is 65B plus the last I look.
That is why shorting/naked shorting should be illegal on non revenue producing companies.