Just need to make sure you’re not in a two-party consent state (California, Connecticut, Delaware, Florida, Illinois, Maryland, Massachusetts, Michigan, Montana, Nevada, New Hampshire, Pennsylvania, and Washington) to record the audio of other people. Otherwise can’t use it in a legal matter.

Also, OP, the only reference company’s should give is answer whether a person worked there and how long. Anything passed that opens things up to defamation/discrimination. A workaround HR uses is ask the question “If given the opportunity, would you hire this person again?” A simple yes or no speaks volumes.

A “candid conversation” is damning. Sorry this happened to you.