It's important to ask

Psychiatric patients are rarely screened for firearm possession.

Researchers found nearly a 10 fold increase in reported access to or possession of firearms when psychiatric inpatients were specifically asked whether they owned or had access to a gun. Researchers suggest involving families or friends in weapons management. However, they also point out that it is more common in the mental health field not to inquire about weapons unless a person has a history of suicidal or violent behavior. This is increasingly becoming a problem for families and friends who are not warned of the risks associated with the untreated symptoms of mental illnesses. It is not uncommon, after the fact to hear responses like this:

McGrath didn't know there were guns in the house, but even if he had, he never dreamed Michael would become violent. …I don't think he ever hit her or threatened to hit her or anything like that.

Base Rates of Firearm Possession by Hospitalized Psychiatric Patients
Dale E. McNiel, Ph.D., Christopher M. Weaver, Ph.D. and Stephen E. Hall, M.D. Psychiatr Serv
58:551-553, April 2007