Pandora (P) has a new major stakeholder.

It's none other than Steven A. Cohen, the billionaire hedge-fund manager whose former firm SAC Capital Advisors, was long a subject of federal investigators prosecuting insider trading.

According to a company filing, Cohen has amassed 12,558,792 shares in Pandora, or a 5.4% stake in the world's largest internet radio operator. Importantly, the stake is a so-called "passive" investment, meaning that Cohen isn't able to use those shares to launch a proxy contest, i.e. to challenge the current board of directors.

Pandora shares were up 1.7% in after-market trading after falling 4.5% to close at $9.50

Cohen made the investment through his firm Point72 Asset Management, L.P., based in Stamford, Conn. The firm is the so-called family office that succeeded SAC, after it pleaded guilty to fraud in 2013 and paid $1.8 billion in criminal and civil settlements with U.S. authorities. Though SAC's CEO, Cohen himself was not required to plead guilty.

Point72 Asset Management becomes the fourth-largest stakeholder in Pandora behind Matrix Capital Management, Corvex Management and Vanguard.

Earlier this week, Pandora secured $150 million in new financing from private equity firm Kohlberg Kravis Roberts (KKR) - Get Report that it plans to use for general operations as it explores strategic alternatives, including a possible sale. The cash infusion came in the form of new Series A convertible preferred stock.

KKR's investment comes as Pandora posted a loss for the ninth consecutive quarter while sales fell short of analyst expectations. Revenue for the quarter ended March 31 totaled $316 million compared with a $317.3 million average forecast. The need for cash was underscored by Pandora's second-quarter sales forecast of $360 million to $375 million which also fell short of expectations of $390 million.

As part of a deal with federal prosecutors, Cohen is not allowed to invest other people's money until 2018, if he chooses to do so.