Karen Read's mistrial motion denied | Officer says evidence changed

Big accusations were made in the Karen Read trial Tuesday — did they stick? Prosecutors' questioning of a dog bite expert led the defense to move for a mistrial, citing activity that was "abhorrent to a fair trial," but it was ultimately denied. Then, a Dighton police sergeant testifies that a piece of Read's now-broken taillight "was intact" when he saw it, soon before state police took custody of the vehicle. Our chief legal analyst explains the arguments behind the mistrial motion and the possible significance behind the taillight discrepancy. Plus, what's a missing witness instruction, and why is the defense asking for it in this case?