It may be fine for him to be there but I was surprised people who seem to strenuously object to a witness seeing new info before testifying didn't object to him hearing all the testimony. But while it may be ok for him to be there, I'm not sure why he had to be there all along. He easily could be asked "X said Y when he testified. Does that correlate with..." without being in court to hear X testify. Perhaps there are other reasons he needed to be there.Kevin Clark is the Director of Crime Strategies and Intelligence for the 4th Judicial District. He compiled all of the state's evidence into these timelines and has been involved with this case since the very early days of the investigation. And a big part of what he's being asked on the stand is... "does this correlate with the same information that (so-and-so) testified to during this trial?" His presence in court was essentially required for the nature of his testimony.
I'm also not sure he's only testifying to "facts" not "opinions" as has been argued in other posts. (Often facts are those things we agree with and opinions are things we don't!) But didn't he say something about not seeing different personalities in L's texts? If so, that was expressing an opinion.
JMO