What NCIS episode is the one where a girl killed by foresnic and he gets put on case to find killer?

The episode you're referring to is called "Judgment Day (Part II)" and is the 24th episode of Season 1 of the TV show NCIS. In this episode, a young woman is found dead in her apartment, and the initial investigation suggests that she was killed by a forensic scientist. However, as the team delves deeper into the case, they uncover a web of deceit and corruption that leads all the way to the top of the NCIS hierarchy.