The Immortal

In 1871 Vol, the discovery on Galtern of the dead body of a foreigner led to the hunt for a mysterious murderer.

Medical Mystery

The corpse, which displayed no obvious cause of death, was taken immediately to a pathology lab for fear that it might carry an unknown disease. Examination of the body revealed no evidence of sickness or any kind of life-threatening condition; the foreigner appeared to have died for no reason. In searching through Galtern's extensive records, the epidemiologists found a handful of similar cases. Instead of closing the investigation, they sent out an inquiry to medical facilities on other islands, asking for information on similar deaths.
At least two dozen records turned up, deepening the mystery. No signs of struggle, no injuries, not even fresh bruises or scrapes were found on any of the victims. There was no pattern to age, sex, life station, or ethnicity. Each case was isolated, ruling out a transmissible disease, and widely separated, ruling out an environmental cause. There were only two common factors in all cases: first, the victims were invariably found in a seated position, or having fallen from one; second, none were native to the islands where they were found. The epidemiology investigation ended with no conclusion reached, and the matter was turned over to Galtern's census office to identify as many of the unknown victims as possible.

Criminal Conundrum

As the census officials combed through records and conducted interviews, an eerie pattern began to take shape. Each identified victim had disappeared several years previously, and many of those disappearances occurred at about the same time and location as another victim's discovery. Even more disturbingly, the pattern extended backward for more than a century. Believing they had uncovered a series of gang-related kidnappings and killings, the census office presented their findings to the investigative arm of the Security Patrol.
The criminal investigation failed to find any evidence of gang activity connected with the deaths. When another victim was discovered on Scaetra in 1878 Vol, the investigators were forced to take the unbelievable position that the crimes were all committed by a single person, termed "The Immortal" because of the timescale over which the deaths occurred. Immediately the patrol sent word to public safety departments throughout the Cluster Islands to treat all missing person cases with utmost urgency.

Seekers' Support

1887 Vol saw at last the first reliable witness to one of the deaths. A Pudarogi streetwatcher, seeing what looked like a man and woman engaged in a struggle, approached them with the intent of breaking it up. Before she reached them, the woman gained the upper hand and the man went limp. The woman carried the man toward a wall, but dropped him and fled when she saw the streetwatcher. Instead of pursuing her, the streetwatcher tried to assist the man; on discovering him dead in the manner of an Immortal murder, she reported a description of the woman. However, the woman--identified as a local resident--was less than 30 years old, and could not herself be the Immortal. The most reasonable conclusion seemed to be that the Immortal had already abducted the woman, and committed the murder disguised as her. Concerned about being misled by appearances, the investigators went to the Eddy to petition the Water Seekers for help tracking the next victim by her aura. A handful of Seekers agreed to assist, and met with the victim's family to get a sense of the aura they were looking for.

Uncertain Ending

The search, the most methodical ever undertaken for a single person, bore no fruit for five years. Then in 1893 Vol a pair of Seekers identified a likely aura on far-flung Barkold, and saw a woman who matched the victim's physical description. The woman ran, and one of the Seekers gave chase. The other Seeker followed after radioing a quick report. She soon found the woman's body, but lost the trail of her companion's aura.
Although the Immortal was never apprehended, that Pudarogi woman was the last victim. The chain of death and disappearance came to an end, and many now believe that the missing Seeker was able to stop the Immortal, even if at the cost of his own life.

The identity of The Immortal remains a complete mystery.  There are no clues to their appearance, age, sex, origin, or even method of killing.
It has been suggested that the Immortal somehow dosed the victims with an unknown poison which would trigger death when the victims engaged in a fight.  This hypothesis accounts for the varying time between deaths, and whoever the victims were fighting with would believe they had caused the deaths, and would almost be expected to flee.
Another suggestion is that some gang was involved after all, but at a safe distance.  The reasoning goes that by framing someone for a murder, the gang would be able to blackmail them into doing further work.  When the mark outlived their usefulness, the gang would arrange their death so as to frame another mark.