A copycat was busted on last week's NCIS installment, but the real sociopath is still in our midst. Tomorrow night, the stakes will be raised, and the casualties may be severe.

After new evidence reveals that the Port-to-Port killer has infiltrated the agency, the NCIS teams chase every lead in a race to track him down on this week's episode.

CBS' promo for "Swan Song," the second to last episode of the season, teases: They Know Who The Killer is. He's Closer Than Ever. He Will Strike At The Heart Of NCIS.

Who do you think the killer is - and who will his victim be this week?

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.