Schiller first returned to the university as a Federal Bureau of Investigation agent and obtained the contract Charles Xavier had signed with the school from the dean.
Although he had been a Visiting Professor, he still had to sign a contract. It contained Charles's personal information, including an address for receiving bills and correspondence. It appeared to be a Xavier family property. Charles's parents should still have been alive in this era, but his current father was not his biological father—it was Stepfather Marco, the man suspected of murdering Charles's biological father, Brian.
Under such circumstances, Charles would never have revealed information about an important friend to his parents, so Schiller had no intention of visiting to ask questions. After obtaining the information on the large house in Westchester, he went to the New York Housing Authority to investigate it. He found that the property's recorded ownership had changed only once. Judging by the dates, it was around the time Charles Xavier's biological father had died, so the change should have been an inheritance transfer.
However, the records had noted the taxes incurred during the transfer. From the amount, it could be inferred that this house was not the only property under Charles Xavier's name. New York also used a progressive tax system in this era; property and inheritance taxes differed for a sole residence and multiple homes. The taxes made it clear whether a house was someone's only residence—the more houses they owned, the higher the taxes.
Judging from the exact amount, this should have been Xavier's second house. In other words, he had another house, and that was most likely where he had settled the local Erik from the nightmare world.
Finding the exact location of that house would be simple. Charles's stepfather Marco was no decent man