CONCORD, N.H. — A New Hampshire state trooper who fatally shot a man at a psychiatric hospital shortly after the man killed a security guard likely prevented further injuries or deaths, the attorney general said.

The trooper, identified in a news release Thursday as Nathan Sleight, fired at John Madore on Nov. 17 after Madore fatally shot Bradley Haas, a state Department of Safety security officer who was working at the New Hampshire Hospital’s front entrance. Madore was a former patient at the Concord Hospital.

Attorney General John Formella said that while his office will follow its normal protocol for uses of deadly force by officers and conduct a complete investigation, the evidence so far indicates Sleight’s actions “were legally justified” under state law, “and very likely prevented further injuries or loss of life.”

Sleight has about 11 years of law enforcement experience, Formella said. It wasn’t immediately known if he was on leave or back at work. Messages seeking comment were left with the New Hampshire State Police and the attorney general’s office. State police also were asked if Sleight would agree to an interview.

A celebration of life service was held for Haas on Monday.

Haas was unarmed. The Department of Safety said this week that unarmed security officers are no longer working at the facility. The state is in the process of contracting with a private company to provide three armed security guards around the clock to screen visitors, patients, and staff.

Other security measures completed include installing fencing to block the hospital’s front entry and direct traffic to an alternate entrance, as well as posting a state trooper and Concord police officer outside the entrance.