The NFL is aggressively investigating allegations that Vikings quarterback Brett Favre sent inappropriate messages and photos to a former Jets employee, according to a source. The investigation is on a fast track. It commenced Thursday, the same day that Deadspin.com posted voice messages and photos that Favre allegedly sent to Jenn Sterger when both were employed by the Jets in 2008. Sterger is reportedly willing to cooperate, but has not yet spoken with NFL investigators.