PLATTSBURGH, N.Y. (AP) — Police said they believe a shooting at a northern New York hospital may have narrowly been avoided after a disgruntled former employee was pulled over with a loaded semi-automatic shotgun blocks away from the facility.

Robert Thibodeau, 52, was arrested Tuesday morning after police in Plattsburgh stopped his pickup truck and found the 12-gauge shotgun with two 10-round magazines and a box of ammunition. The stop was made after a brother told police that Thibodeau had recently been fired from Champlain Valley Physicians Hospital in Plattsburgh and made comments about returning there to harm people, according to the Plattsburgh City Police Department.

Chief Peter Mitchell said Wednesday that police believe Thibodeau intended to use the gun at the hospital.

Clinton County Sheriff David Favro told the Press-Republican of Plattsburgh. that “this is about as close as I’ve seen to what could have ended up in a mass casualty situation.”

“There’s a lot of details that will unfold with further investigation. But definitely he had the means with him, and he certainly could have accomplished mass casualties with his weaponry, and that would have been a horrible situation,” Favro said.

Hilary Rogers, chief assistant public defender for Clinton County, said she had no comment on the ongoing case.

Thibodeau’s vehicle was intercepted by a patrol officer as it headed toward the hospital, which is about 30 miles (48 kilometers) south of the U.S.-Canada border. Thibodeau initially failed to pull over when the officer put on emergency lights and then did not immediately comply with orders to leave the vehicle. He was eventually taken into custody with help from multiple police agencies without further incident, Plattsburgh police said.

Thibodeau entered a not guilty plea Tuesday to one count of second-degree criminal possession of a loaded firearm and was remanded to jail after his arraignment.

Mitchell praised the brother for taking action.

“He’s one of the biggest heroes in this, to make that decision,” Mitchell said, “to notify us and get it taken care of before he got to his location.”