I expect that the current Person of Interest is a red herring. Red Robes was simply a simulacrum ... of Zach. The reasoning follows:
- Zorian only detects two souls when searching for the mark.
- Zach had previous access to the spell.
- Simulacrums that remain alive beyond a day or so have a distressing tendency to become unstable, often attacking their originals.
- Zach's mind and memory have been modified - by Red Robes, in fact.
- Zach's power growth and shaping are off by a factor of two. He has magnitude 50 mana, but magnitude 25 shaping. A simulacrum might double the growth of mana, meaning Zach was originally a magnitude 25 mage.
- Zach's memory and soul modifications may have prevented him from feeling what magic Red Robes was using.
- Red Robes' attacks may well have been intrinsic Controller abilities which did not consume mana at all.