A former trader-turned-informant secretly recorded more than 125 conversations with ex-colleagues at hedge fund firm Visium Asset Management LP, according to a court filing. The informant, previously identified by Bloomberg News as junior trader Jason Thorell, spent more than two years cooperating with the Federal Bureau of Investigation and the U.S. Securities and Exchange Commission. He is identified in court papers only as “CC-1,” or co-conspirator-1. Thorell didn’t return a text message to...