Embattled hedge fund manager Scott Sacane was a big net seller of

Esperion Therapeutics

(ESPR) - Get Report

in July, reversing his trading strategy from a month earlier, new federal filings show.

Sacane's Durus Capital Management belatedly disclosed all of its trading in Esperion and another small medical company,

Aksys

(AKSY)

, in a cascade of filings with the

Securities and Exchange Commission

that just became public.

The filings depict Sacane's frenzied trading in the two small-cap companies over a period of two months, with the fund often buying and selling large chunks of their shares on the same day. The trading wouldn't be that out of the ordinary for a modern hedge fund but for the fact that Durus ran up huge, and until recently, undisclosed stakes in both companies -- and said he did it inadvertently, leaving some to question his motives.

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In July, Durus generated gross proceeds of $34.8 million from selling Esperion shares. In the same month, it spent $9.5 million acquiring the same company's shares, according to the recently filed trading records.

It's impossible to calculate Durus's profit or loss on the trades since his cost basis isn't known. Still, the fund generated proceeds of $25 million from all its buying and selling of Esperion shares in July -- a time when the stock generally was trading around $19 a share.

In June, when the stock traded between $13 and $16 a share, the ratio of buying to selling by Durus was reversed. Trading records show that the hedge fund shelled out $31 million that month to add Esperion shares, while it generated $19 million in proceeds from selling stock.

A rough analysis of Durus' trading activity for those two months reveals that the hedge fund generated net proceeds of $13 million from all of its trading in Esperion's stock (again, his net profit or loss on the trades isn't known).

On one level, Durus' activity over the past two months is no different from what any smart trader tries to do: buy low and sell high.

But the buying and selling in Esperion came at time that Durus failed to disclose its ownership stake in the cardiac-care drugmaker had risen from a little over 22% to more than 33%. Sacane contends the failure to disclose that information was an error, but he has not explained how the fund "inadvertently" purchased so many shares. The stake in Aksys grew much greater, to more than 70%.

Others on Wall Street are less charitable, and argue the Sacane fund must be guilty of either gross incompetence or an attempt to manipulate stock prices and boost its performance.

No agency is known to be investigating Durus and there's no overt evidence he marked up any stock. Still, a look at his trading in Aksys reveals a day-to-day involvement that is unusual in a single issue, even for a hedge fund.

Sacane bought a total of $41.2 million and sold $5.3 million of Aksys from July 1 to July 24 -- a period when the shares climbed steadily from about $12.50 to $15. Assuming an average price of about $14 a share, Sacane's fund would have bought or sold roughly 3.3 million shares during that period. That's more than half the roughly 5.7 million total shares that traded in the stock between those dates.

Meanwhile, the apparent profit generated by Durus from its recent trading activity in Esperion shares could be a boon to Esperion. That's because federal securities laws require any 10% owner in a stock to return to the company any profits made on a short-term purchase and sale of that stock.

While it's too soon to say how much of Durus' apparent profit Esperion may be entitled to, a company spokesman said the drug manufacturer is reviewing its options. A spokesman said Esperion would pursue collecting any of Durus' trading profits it is entitled to collect.