Who murdered a marine with nerve gas?
That was the big question on NCIS: Los Angeles Season 9 Episode 21 as the forensic investigation sent the team down various different avenues.
With that, NCIS and the FBI joined forces to find a way to take down the killer.
However, it quickly became apparent that there could be more victims popping up along the way.
Did the team find out all the details before it was too late?
Use the video above to watch NCIS: Los Angeles online right here via TV Fanatic.
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Paul Dailly is the Associate Editor for TV Fanatic. Follow him on Twitter.