Ayla is the one that solves the problems the police want to ignore or sweep under the rug. The role of Speaker for the Dead was created years previously after so many police shootings went unanswered. It was a combination of oversight committees that were supposed to police the police and groups like Black Lives Matter.
The federal government (this was still when the USA was one entity) created a position of Agents that could go into any jurisdiction and investigate any case that looked like it was being pushed to the side. For years they held a lot of power in law enforcement, but over the years the position was not filled on a regular basis and as the government experience other problems the Speaker of the Dead became almost an urban myth to a lot of people. But the role still exists, even in parts of the country that aren't part of the USA anymore.