<human>: Can you condense the text into three sentences or less?

Several people around the lab have been interviewed in person by a contract investigator -- his business card lists him as "Office of Personnel Management".  The back of his card includes the following:

"Privacy Act of 1974
The Privacy Act provides that the information we discussed, including your identity, will be written in a report of the investigation.  That report will be furnished to the agency requesting the investigation, other agencies as warranted, and to the person investigated upon his or her request"

The guy they are investigating is an amoral prick.  If I elaborate on his poor qualities (lying, manipulating, etc), is that considered libel?  I have never talked to an investigator before.  Is this standard practice for certain jobs?  The guy being investigated is a scientist. 

The whole investigation seems odd.  He abruptly left work here to go to a huge chemical company, and has changed jobs again recently.  I *think* that the investigator was hired by the large chemical company which has a reputation for being legally active.
<bot>: How do I protect myself when being asked questions by an investigator?  I don't want to paint a rosy picture of a terrible person but I don't want to get into any legal tangles either.