The Source is an object mentioned in F.E.A.R. Perseus Mandate.
F.E.A.R. Perseus MandateEdit
The Source is first mentioned by Armacham Technology Corporation employee Brett, who asks Davies to put together a team to remove it. When Davies doesn't understand what the Source is, Brett tells him to forget he said anything and that he'll remove the Source himself. It is also revealed that the Nightcrawlers are after the Source. The Sergeant can later find a laptop that reveals that the Source is Paxton Fettel's DNA.
At the end of Perseus Mandate, it is revealed that the Nightcrawlers managed to recover Fettel's DNA and turn it over to the Senator.