Require that all gun purchasers and owners pay for and pass a pyschiatric evaluation prior to obtaining a gun.
The psychiatric evaluation should screen out to the extent possible dangerously mentally ill people and those with signs of a psycopath by a testing system to be determined by the mental health professional community or organization such as the American Psychological Association.
The screening should include, but not be limited to, an interview of the purchaser by a licensed mental health professional as well as dialogue between the mental health expert and close family members and friends of the gun purchaser to verify to the extent possible the sane mental health of the purchaser.