The Colorado Department of Health is investigating Memorial Health System for using a Taser to subdue a patient earlier this year.

A statement from the hospital says it “treated a homicidal patient in the Emergency Department who became physically violent and threatened our staff…. A Taser was used on this combative patient in compliance with policy and to protect the patient and care providers from being injured.”

The investigation was triggered when the patient complained to the state. Hospital officials said the patient was not restrained at the time of the incident, despite reports to the contrary.

The state’s findings are not complete, but hospital officials say they’ll use the review process as a chance to evaluate its policies and procedures on using Tasers.

Memorial sees more than 130,000 patients a year in its emergency departments, and cited a study by the Emergency Nurses Association that claims more than half of the nation’s emergency department nurses had been physically assaulted at work.