As I understand the facts, the TSA lawyer was sending them transcripts and was also talking about lines of cross-examination they would likely face. The former is a serious no-no. The latter, if handled right (preferably by part of the prosecution team and not some TSA dunderhead) would probably be OK. I have prepped hundreds of witnesses, and it isn't that hard (and doesn't violate court restrictions) to make them indirectly aware of what you can't say to them directly. It does, however, take some skill and sensitivity, which obviously were lacking in the TSA Allstar.
If that's true, it was a major blunder. Witnesses must be shielded from prior trial testimony. That's basic.