A car crashed against a commuter train, causing the death of 15 people (16 if you consider an unborn child a casualty). The car was owned by a piece of work who get used to faking car plates to avoid expensive speeding tickets. Anyway the vehicle was actually stolen by someone else in the early morning and the thief broke down the gate in order to get among rails. The attacker left the car shortly before the collision occurred, hiding himself between the wounded people. Detectives started a manhunt and after some interviews they caught a mild middle aged man who had just separated from his wife and fired from his job (despite the business is run by his brother), now living in a bedsit. He attempted to commit suicide several times, so it's the right profile, but he could be released due to his mental condition.
Casey is freaked out again for having witnessed a boy dead right after he had bumped into the crime scene (he's fathering a boy of the same age). We make acquaintance of the new junior district attorney who takes the place of Philips, just promoted in another courtroom. Thorne doesn't seem to get along with her.