Source: The Trouble with Secrets, pg(s). 3-4
Aygrim Bossell is a largely retired member of the Pathfinder Society working as a record keeper in the Pathfinder Lodge of Sothis, Osirion. He is mostly senile, but kept in his position by Venture-Captain Norden Balentiir.
Aygrim was contacted decades ago by an old lover and fellow Pathfinder, Taylin Harkus, who had been attacked and begun the transformation into becoming a vampire. She plead with Aygrim for help in curing her of her impending undead state, and he agreed to find clerics and researchers to assist him, returning with her to a basement room in the Sothis Pathfinder Lodge. When he returned a week later, however, the new team overpowered the young vampire, tied her to a table, and began performing cruel experiments on her. Bossell ignored Harkus' pleas for help for eight days until he heard screams coming from the chamber where they had her imprisoned. Rushing in, he found Harkus free of her restraints and tearing the other researchers apart. Fearing for his life, Aygrim locked the door to the experiment chamber, leaving the other researchers to their doom.
Knowing that his actions would not be seen in a positive light by other Pathfinders, Aygrim did his best to cover up the whole affair. He boarded and then walled-up the room where Harkus was still imprisoned with the researchers (now transformed into vampire spawn), explaining his actions as necessary to prevent the spread of a magical disease he had discovered. He also forged documents showing that the doomed Pathfinder researchers had been lost on various other assignments, and tried his best to forget it all.
Later in life, Aygrim's conscience began to prick him, and he wrote down his foul misdeeds in a journal he kept secret, but never mentioned that Harkus was a vampire. Not wishing to throw him out into the streets, and unaware of his foul betrayal, the current venture-captain of the Sothis Pathfinder Lodge, Norden Balentiir, kept Aygrim on as a record keeper. For 60 years, Aygrim guarded his secrets, but eventually began suffering from senility and forgot much about his past misdeeds.
Worried about his failing health, Aygrim's servant Fendel searched among his belongings for a will, and inadvertently found the secret journal. Curious to discover if the tales of his master's dark past were true (and unaware that Harkus was a vampire and could still be active), Fendel opened the bricked-up experiment chamber, but was quickly overcome by Harkus and her progeny.