“That could save a lot of lives,” said Dr. Swanson, a member of the consortium.

Varying Interpretations

One place that has an intimate awareness of the dangers of guns, especially in the hands of people struggling with mental illness, is Arapahoe County in Colorado, where 12 people died in the Aurora movie theater rampage last year. And at a high school there just this month, an 18-year-old gunman critically injured another student before taking his own life, though there has been no indication that mental illness was a factor.

Still, when it comes to seizing firearms, the sheriff there, Grayson Robinson, says he is also acutely aware of the legal limitations. If his deputies encountered a man on the street with a gun acting irrationally or suicidal, they would probably confiscate that weapon for safekeeping, he said. But they would not have the legal authority to enter his home and even temporarily take any other guns. Nor would the authorities hold on to the confiscated weapon, he said, unless the owner is expressly barred by law from having it.

“We understand property rights,” he said. “We would return those weapons to him upon his request.”

In the absence of specific guidance under federal and state laws, local police departments vary widely in how they deal with the issue, The Times found. Some hew to a strict interpretation. Others appear to be searching for a middle ground, fearful of what may happen if they return guns to dangerous people but also aware that they are on difficult legal terrain.

In Arapahoe County, the Sheriff’s Department has confiscated weapons from just 13 people it sent for emergency psychiatric evaluations in the past two years, records show. In 10 of those cases, the guns were returned to their owners. (One gun was scheduled for destruction at the owner’s request; another was given to a third party; one recent seizure was still in the department’s possession.)

Among the guns seized was the pistol from the bathrobe pocket of Mr. Santiago, the veteran found walking around his home in a trance in November 2011. It took five minutes after deputies arrived for Mr. Santiago, then 23, to emerge from his catatonic state, according to the incident report. When he came to, he asked if he had hurt anyone. He also told deputies that he had post-traumatic stress from his deployment in Afghanistan and had experienced a similar episode before. The Fire Department took Mr. Santiago to the hospital for a brief stay to be examined, and sheriff’s deputies took his gun. It was returned the following March.