Having tried 265 criminal jury trials to verdict in the U.S., I can tell you jurors having a “change of heart” is not as unusual as you might think. It happens often enough that competent trial judges and prosecutors know how to solidify a jury verdict. Polling the jury in open court and on the record is now done in almost every trial. Unless there was clear misconduct in the jury room, a guilty verdict with all jurors acknowledging their agreement on the record is hard to overturn. It can, and has happened, but it is exceptionally rare and requires clear evidence of misconduct. A change of heart or a changed mind after the fact isn’t enough. Again, this comes up more often than one would think and it is usually dealt with swiftly.