After his escape from Gentek, Mercer could not remember his past. However, he managed to find his sister Dana after he absorbed the memories of a Blackwatch soldier.
When they were safe from Blackwatch and the Marines, Dana suggested that Alex should look for clues at his apartment. Unfortunately for Alex, Blackwatch knew he was coming. When he recovered from the flashback, Blackwatch agent Captain Mac Marshall gave the order to blow the hidden bomb. Alex survived the blast, though, and continued to hunt down Mac Marshall. Whatever possessions Alex had in his apartment were destroyed due to the explosion.
In his apartment, if one looks closely at one of his walls, he seems to have a whiteboard meaning due to working on the Blacklight virus, he has a formula showing the makeup and schematics to its design, and it has a chemical composition visible on the board.