Warning! Spoilers ahead for Infinite Frontier #0
Future State event. For example, Infinite Frontier #0 seemingly just revealed the identity of the man who will one day become Peacekeeper-01, otherwise known as the man who killed Batman (but not Bruce Wayne).
In DC's Future State, Gotham City is taken over by the organization known as the Magistrate, who rapidly turn Gotham into a fascist police state. Any kind of mask-wearing and vigilantism is illegal and punishable by immediate execution by the Magistrate's elite force known as the Peacekeepers. Naturally, Batman becomes Public Enemy No. 1, and Bruce Wayne is targeted for execution by the organization's leader Peacekeeper-01, who somehow knows that Wayne and the Dark Knight are one and the same. However, Wayne manages to fake his own death, making PK-01 believe that he has been successful in killing Batman. This allows Bruce to work in the shadows to bring the Magistrate down as the new Dark Detective.
Additionally, further issues of Future State issues set in Gotham see PK-01 carrying a personal vendetta and obsession with Batman, going beyond simply following the Magistrate's mandate. However, it remains a mystery as to the reason for this hatred, even with the conclusion of Future State: Dark Detective. Now, present-day Gotham in an Infinite Frontier #0 story written by James Tynion IV with art by Jorge Jimenez holds the answer with the devastating attack and explosion at Arkham Asylum. While Batman is rushing to get to the Asylum in time, he fails to save one Sean Mahoney, an Arkham guard who risks his life to save the facility's nurses before the building explodes, getting severely injured himself.
Based on the rare times PK-01 is seen unmasked, it does appear as though Mahoney is the man who will be recruited into the Magistrate and eventually become its leader. Given the unrest and tensions towards Batman and vigilantes in Gotham, it's possible that Mahoney may grow to resent Batman as well due to his serious injuries, thereby providing the personal motivations PK-01 carries in Future State. Furthermore, as James Tynion IV and Jorge Jimenez' Batman series continues to reveal the seeds of this dark future, it seems likely he'll be approached by Simon Saint and his Magistrate Program to be their first Peacekeeper, as he'll no doubt become a popular public figure and ideal candidate due do his heroics in Arkham, which will be starkly juxtaposed with Batman's recent failures.
While it's been made clear that the events of DC's Future State are not set in stone, it does seem as though Sean Mahoney is the man who will become PK-01, provided Gotham stays on the same course towards the Magistrate's control in the coming years. This would also mean that Batman has inadvertently orchestrated his own demise (more than he already has). If he had just been able to get to Arkham earlier, he could have saved Mahoney before the explosion that rocked Arkham and sent him on his dark path in Infinite Frontier #0.
