"Expert" testimony on technical matters is a whole 'nother ball of wax - nothing to do with what I'm talking about.
The reality is that a great deal of what juries believe comes from outside experiences; they've been lead to believe eyewitness testimony and eyewitness IDs are very reliable, and if you believe the witness is not lying, then their testimony is automatically correct.
The reality is, based on scientific study, and the history of these cases, is that there should be reasonable doubt about ALL eyewitness testimony. I'd have a hard time convicting someone when that was the only or almost the only evidence.
And the academic studies showing this aren't from "hired gun" expert witnesses - just scientists interested in studying human memory.
One famous demonstration done in large psychology lecture classes is the professor hiring an actor to come in and steal something (without telling the class beforehand.) The incident happens and the students are asked to write down what the actor was wearing, what happened, etc. When they're reviewed, everyone reports wildly different clothing, appearance, sequence of events, etc, with most of them being very wrong.
Another really interesting one is plane crashes - time and time again, eyewitnesses will report crashing aircraft being on fire, when they were not (and often there is a videotape clearly showing no fire on the aircraft.) It's apparently a phenomenon where the brain inserts a false memory to make sense of viewing a traumatic experience.
I've participated in that exercise myself, and while there were wide variations of what descriptions were voiced, there were certain traits/characteristics/observations that were observed by MORE than half the group, although ALL details were not consistent to that extent. This results basically from what individuals tend to focus on, as opposed to mis-interpretation (at least in the instance of my participation).
I also participated in a "mock jury trial" for a certain widely-recognized attorney, and as a Defense Attorney, the appeal to emotion and attacks on personal basis of witnesses is the same style I saw in a 3-month-sequestered trial I was a juror on, of 5 organized crime defendants. Although in both instances, I was somehow selected as the jury Foreman, it was consistent where individuals enacted their personal biases and attempts to empathize with either a defense character or a prosecution character, and this becomes abundantly obvious in the Jury Room.
The OJ verdict, I'm sure, would have been expected by more people had they been aware of the Jury composition. Hence, Jury Experts have become nearly as critical as the Defense Attorneys themselves.
The jury system has degraded to the social-engineering-opportunity to most who serve now on juries, and it shows clearly in the civil suit verdicts.
Criminal verdicts are so un-predictable that plea bargains have become the only mechanism the Prosecutors have now to assure SOME measure of penalty can be gained, rather that to risk a rogue jury verdict and gain no measure of Justice. There's only Appeal opportunity for Defendants, which further skews the process.