So, basically it was a Spirit of Man, right? What was his power? Equal/lower/greater than Griffin's? Can he recognize his signature afterwards? What about astral tracking? What does my knowledge tell me? Can I roll for Magical Threats/Spirits for additional info?
And - is this place a Mana Ebb (lower Bacground Count of -3), or a poluted Aspected Domain (higher BGC of +3)?
Ok translated to game terms:
Spirits force - greater than Griffins
Signature: Yes, If you see it again, you will be able to recognize it
Tracking: Imposible, the link is not a part of signature (strange, but true)
Domain is naturaly aspected to toxic: +2, and was manipulated to amplify this: +1 =+3
Magical Threats: Based on indications given it is Toxic spirit.