NEW YORK — Billionaire Steven A. Cohen has been in the crosshairs of federal prosecutors for nearly a decade. His hedge fund, SAC Capital, was once one of the most powerful on Wall Street, managing more than $15 billion for investors and producing stellar returns for years.

But prosecutors suspected that SAC’s success was too good to be true.

U.S. Attorney Preet Bharara in Manhattan once called Cohen’s hedge fund as a “veritable magnet for market cheaters.”  When, in 2013, SAC agreed to pay $1.2 billion to settle charges that it tolerated rampant insider trading it was one of the highest-profile successes in the government’s aggressive push against insider trading.

Still, connecting Cohen, one of the richest people on the world, directly to those misdeeds has remained elusive. And on Friday, the Securities and Exchange Commission essentially conceded. The Wall Street watchdog settled its nearly three-year old civil case against Cohen, who was accused of failing to properly supervise employees, with no financial penalty.

Instead, Cohen’s new firm, Point72, which manages his $10 billion personal fortune, must hire an independent consultant to make sure it complies with securities laws. Once at risk of being banned from the industry for life, Cohen can begin managing others’ money again in 2018, under the agreement.

“It’s the ultimate slap on the wrist, if he’s smart in two years he [Cohen] will be back managing money,” said Gene Murphy, a white-collar defense attorney at Murphy & Hourihane in Chicago.

It is a remarkable turnaround for one of the most recognizable people on Wall Street. Even as he lived under federal investigation, Cohen remained an influential figure with industry insiders closely following which stocks he bought and sold. When Cohen spent $155 million for a painting by Pablo Picasso titled “Le Reve” just days after SAC settled with federal regulators it was covered in the local tabloid press.

“Inevitably, some will ask why I agreed to settle,” Cohen said in a letter to Point72 employees obtained by The Washington Post. “The longer the pending litigation lingered, the more it distracted from the world-class Firm that we are building.”

“When SAC pled guilty, I vowed that what happened to SAC would never happen to Point72,” Cohen said in the letter to employees. “It is a testament to your perseverance, talent, and focus that we not only survived an event that would have ended most firms, but we thrived in the wake of it.”

The settlement is a humbling end to one of the government’s most high-profile cases. The allegations against Cohen weakened last year when prosecutors were forced to drop its case against former SAC employee, Michael Steinberg. Steinberg, a longtime Cohen confidant, had been found guilty of trading on illegal tips involving technology stocks. But prosecutors abandoned that case and several others after an appeals court decision made it more difficult for authorities to purse certain kinds of wrongful trading cases.

For a while, the SEC appeared poised to continue to pursue Cohen by focusing on his alleged failure to supervise another employee, Mathew Martoma, who was convicted last year of what prosecutors described as the most lucrative insider-trading scheme ever. Martoma is appealing his conviction and Cohen did not acknowledge wrongdoing in Friday’s settlement.

“Insider trading cases have always been difficult to make, but with the [appeals court ruling], the SEC was dealt an incredibly tough hand, and the deal with Cohen is probably the best it could have hoped for under the circumstances,” said Jordan Thomas, a partner at Labaton Sucharow and a former Justice Department trial lawyer.