In addition his unusual appearance, the Blank is resistant to harm and capture. He walks away from gunfire or other assaults that should have been fatal. Magic likewise seems unable to effect him directly.
What is unknown to the authorities (and perhaps everyone but the person who currently has it) is that the blank effect is the result of a magic item: A silvery dinner suit, flashy like something a stage performer might wear. When the suit is donned, the person wearing it can watch in a mirror as they "fade" into the blank.
Attempts to discover the suits origins prove fruitless. The tag is worn, but appears to list it's manufacturer as "NOX." No clothier of that name is known.
In addition to making the wearer unrecognizable (and having the side effect of distorting their voice), the wearer has AC 0 and takes half damage from any mundane weapon. Magical weapons deal "normal" weapon damage without any bonuses. The wearer is also immune to any directly aimed magic. Magics that deal damage through a physical effect (like a fireball) can effect the wearer at half damage.
While wearing the suit an individual is able to perceive the etheric layers of the Material plane and with experience, the near Astral. The kaleidoscope of lurid colors and outre images can be highly disorienting until a wearer become use to it.