I think there's a secondary issue that should be at play in this case (I haven't read the opinion, so they might have addressed this). Independent of the 5th am

I think there's a secondary issue that should be at play in this case (I haven't read the opinion, so they might have addressed this). Independent of the 5th amendment, prosecutors are generally not allowed to introduce prejudicial evidence, or evidence that would exploit the irrationality of humans more that provide actual evidence. It feels like this type of body language analysis would qualify. Perhaps if there was someone with training in body language, and he could cite research generally accepted by the scientific community, that his method of analysis produces reliable results, then this may be admissible. Of course, they should also maintain a recording of the interview so the defense can use it, and to mitigate the potential for human failures. The cost of this seems negligible, so the only reason I can see them not doing this is if they don't want the full account of what happened precisely to be shown.