Like Mr. Pean, patients seeking help at hospitals across the country have instead been injured or killed by those guarding the institutions. Medical centers are not required to report such encounters, so little data is available and health experts suspect that some cases go unnoticed. Police blotters, court documents and government health reports have identified more than a dozen in recent years.

They have occurred as more and more American hospitals are arming guards with guns and Tasers, setting off a fierce debate among health care officials about whether such steps — along with greater reliance on law enforcement or military veterans — improve safety or endanger patients.

The same day Mr. Pean was shot, a patient with mental health problems was shot by an off-duty police officer working security at a hospital in Garfield Heights, Ohio. Last month, a hospital security officer shot a patient with bipolar illness in Lynchburg, Va. Two psychiatric patients died, one in Utah, another in Ohio, after guards repeatedly shocked them with Tasers. In Pennsylvania and Indiana, hospitals have been disciplined by government health officials or opened inquiries after guards used stun guns against patients, including a woman bound with restraints in bed.

Hospitals can be dangerous places.