Joseph Welch was the husband of Constance Welch and had two children with her. At the time of his children's death and his wife's suicide, he was an associate manager working the graveyard shift at the the Frontier Auto Salvage Yard when he was 30. This and other information can be seen in a newspaper that Sam views when searching for information about who the Woman in White could be.
When Sam goes to question Joseph, he is a shadow of his former self. He still appears to be very distraught about his wife and children's deaths, having moved away from their house after she died. When Sam hints that Women in White originate from their husbands' having affairs, going insane and killing their children because of it. Joseph becomes very angry, and, though he hints at an affair when he admits that he "may have made mistakes," he is certain that Constance would have never hurt his children.