Fontaine

Hint 1 of 5:

Mason - I negotiated with the doctor; Black December deemed you a threat.

Hint 2 of 5:

McBain - Black December arranged for his death, but I did not do it.

Hint 3 of 5:

Scorpio - A remarkable agent. He died 18 months ago in Lebanon.

Hint 4 of 5:

Thunderbolt - It will happen soon.