MONTPELIER, Vt. — No criminal charges will be filed against police officers involved in the fatal shooting of a bank robbery suspect on the grounds of a high school, state prosecutors said on Tuesday.

Robbery suspect Nathan Giffin was carrying what appeared to be a handgun and ignored repeated orders to drop it while telling officers he would not surrender because he did not want to go back to prison, officials said. Police engaged in a more than hourlong effort to get him to drop the gun so the situation could be resolved peacefully, they said.

Giffin, who authorities said had just robbed a credit union, told the officers, “I’m not putting this gun down for nothing. Do what you got to do.” He then moved around a shed and advanced toward them, they said.

Eight Vermont state troopers and one Montpelier police officer fired nearly two dozen rounds at Giffin from handguns and rifles, officials said. Giffin, 32, was hit seven times and was pronounced dead at a hospital shortly after.

What had looked like a handgun Giffin was carrying turned out to be an unloaded BB gun, officials said.

“I don’t think anything could have been done differently at the scene,” said state Attorney General T.J. Donovan, who held a news conference in Montpelier, where he announced the results of his investigation and that done by the office of the Washington County state’s attorney.

While prosecutors will not be filing charges, the head of the state police, Col. Matthew Birmingham, said that as a result of the Montpelier shooting and others his agency would update its use-of-force policies and practices.

“Tactics and technology in this discipline are always evolving and improving,” Birmingham said.

Last week, the state police announced a change to their policies that would require troopers involved in shootings to take more time off before returning to duty.

As a result of the review, the state police will be training troopers in more de-escalation techniques, adopt new use-of-force policies and acquire more non-lethal ways to resolve such encounters, such as plastic projectiles and bean bags that can be fired at suspects. All members of the state police tactical teams will be outfitted immediately with body cameras, and the agency will work to get body cameras for all troopers.

And now that the criminal investigation into Giffin’s Jan. 16 shooting on the grounds of Montpelier High School has been completed, the state police will conduct an internal review to determine if the actions of the troopers involved were justified.

All but one of the troopers involved have returned to duty. The other trooper, who fired four shots at Giffin after another officer opened fire first, also was involved in fatal shootings on Sept. 1 and Feb. 11. He is on administrative duty pending the results of the ongoing investigation into the February shooting, Birmingham said.