It fits with what I want to see....

Liz gets suspicious of Jake (which she already is) then starts snooping and finds out who Jason really is.
I'm thinking the PI would be Scammy because Spin was always, like you said, the more active one and unless he comes back I can only see her as the PI. Given the storyline if Skank dug deeper, she would have found out about Jason.
The hitman will have to save her? Will Liz be in danger from finding the truth.....

If I remember correctly, Liz finding out about Ben wasn't her snooping, she found out by accident..... I wasn't really watching back then just some clips, so I'm not sure but I don't think Liz was suspicious and went snooping