Dan "Daniel" McLane was a Congressman and also a former NIS/NCIS Special Agent who is the first murder victim in Crescent City (episode).
He was one of the Fed. Five, and famous for deducing and apprehending the "Privileged Killer." In actuality, however, he had accepted a bribe from Josef Hanlon to frame another businessman with being the serial killer to protect the latter's son, Spencer Hanlon, the true serial killer, as his wife and child had been dying from a disease at the time. He also received several "campaign contributions" as hush money to keep his silence.
Eventually, he decided to come out and tell the truth about what happened.
Unfortunately, Josef learned of this and contacted his son, Spencer with Spencer eventually murdering McLane with his signature M.O., and proceeded to dump him into the river where he was eventually discovered with NCIS Special Agent Dwayne Cassius Pride being left devastated upon learning of McLane's murder.