A cop (Gerald McCullouch) was murdered while performing his duty. He was posted in a Jamaican neighborhood, protecting a witness in an upcoming drug trial. He turned out to be Eames' husband old partner and this caused the detective a little breakdown (her husband, Joe, was an uncover officer shot dead by gangs years before). The victim was also the star witness in Joe's trial and after the perp shot the second (and last) witness, a local low profile drug dealer, it was easy to find out the connection between the two murders. Eames started digging in the old evidences and thanks to improvements in DNA checking, she was able to prove the wrong guy spent nine years in prison. At the end both murder cases were solved.
A nice episode, illustrating the pressure that sometimes detectives must face to find as soon as possible the cop killer. They had to put the blame on someone right away, making mistakes in the process.