Azzrukhan

"Azzrukhan the Banished Blade", as per the bloody banner found near him.

Graal Lark's killer, he left a Brimstone of Accelerated Decay on his body. He had 3 more, as well as Lark's recording eyestone, on his body.

A Flayhorn disguising himself as a Disciple library aide. Accompanied by four Fiendish Gargoyles. Killed Graal Lark as part of a trap (alledgedly) for Riga, whom he and his group of devils identify as the "key" to their return to the Nine Hells, after being "exiled" onto the material for centuries.

Answers to Zarzathel.

Unlike normal Flayhorns, he was more vulnerable. His autopsy and examining his aura revealed that he seemed "incomplete" as a devil. Ordo describes him as a "flesh puppet", while Riga theorizes that it may be due to prolonged sojourn on the Material plane. Quite tellingly, his corpse did not vanish, melt nor combust at first.

Once the core fragments were removed from his chest, a lazy flame blackened the outside of his corpse, but it wasn't a full disposal.