US prosecutors have concluded that they don't have enough evidence against hedge fund billionaire Steven A Cohen to file criminal insider-trading charges against him before a July deadline, people familiar with the situation said.

Investigators probing the biggest alleged insider-trading scheme in history have been eyeing the 57-year-old Cohen and his namesake SAC Capital Advisors hedge fund firm for a decade, suspicious that some of its trading profits were too good to be legitimate, according to people close to the probe.