If he is smart, he will require his lawyer be present and have the whole interview video taped .... else no interview.
The policy of the FBI is to not allow their interviews to be recorded. I've read of many instances where the FBI has invited people to come in for an interview, for whatever reason. If the person's attorney rejects the FBI's demand that the meeting not be recorded, the FBI all of a sudden loses interest in interviewing the individual, and the person never hears from the FBI again. Works with the IRS, too. Had a phone conversation with an IRS revenue agent on the phone about 18 years ago. After the agent lied about a few issues and refused to answer a few questions, I asked if the called was being recorded. He lied and said it wasn't. I then asked him if he would like me to send him a copy pf the recording of our call, he quickly declined and hung up. Haven't heard from the IRS since that time.