Authorities face mounting questions about how a gunman with a history of mental illness, an array of weapons and who police knew had a potential for violence was still able to own guns and commit the deadliest mass shooting in Maine’s history. Robert Card was identified as a person of interest about four hours after he shot and killed 18 people and wounded 13 others last week in Lewiston, Maine. He was found dead two days later. The intensifying scrutiny over Card’s access to firearms underscores how hard it is to seize guns from possibly dangerous people with mental illness.