Honestly, I think Donald Love could be Mr. Nasty. Think about it, the guy is weird and very extravagant, since in GTA LCS in two missions he sends us to steal a body inside the Romero vehicle, then he sends us to steal the corpses of Ned Leeds, an unscrupulous journalist who cheats Toni Cipriani, the protagonist, in the plot, and Avery Carrington, his former teacher that many may know about GTA Vice City, on the occasion of a supposed party in a hangar, in addition to that before during the Staunton Island missions we can observe him eating a human torso . In GTA III, corrupt detective Ray Machowski mentions that Donald is a guy with strange tastes and money to pay for them, theorizing several fans that maybe Donald could be cannibal or necrophile, a profile that could certainly fit in with someone like Mr. Nasty, mainly for the snuff movies it produces.
What do you think?

Very interesting theory! Personally i think Schaffer is one of the most mysterious characters in Manhunt franchise