Two troopers have been placed on administrative leave pending completion of a state police investigation into an officer-involved shooting Tuesday that left an elderly man dead, authorities said.

Walter Wiemann, 73, died of injuries at a Pittsburgh hospital following an armed standoff that began shortly before noon Tuesday, at his house on Nursery Road in Forward Township.

State police said Wiemann aimed a rifle at tactical team members before one of the officers shot him.

He was later flown to UPMC Presbyterian hospital where he was pronounced dead at 4:52 p.m., according to the Allegheny County Medical Examiner's Office.

Authorities said a cause of death was pending an autopsy. The medical examiner's office in an email did not indicate when the autopsy would be performed.

Butler County District Attorney Richard Goldinger said that as of 1:30 p.m. Wednesday he had not received any autopsy findings. He could not be reached later Wednesday for an update.

The DA's office is assisting in the police investigation.

Troopers from Butler were called at 11:47 a.m. to the home for a man “making threats to himself, others and police responders,” according to a police report.

The 911 log said the man, later identified as Wiemann, reportedly had dementia and “might be armed.”

Police said Wiemann is married but he was alone at the house during the standoff with police.

The first troopers there saw Wiemann go into the garage, police Cpl. Tim Morando said Wednesday. Police repeatedly tried to make contact with Wiemann but to no avail.

The Special Emergency Response Team was subsequently activated while police held the perimeter around the house. The team is comprised of troopers from different stations across Western Pennsylvania.

A police helicopter was also called in. Additionally, four negotiators were on scene, Morando said.

No communication, however, was made with Wiemann during the standoff.

SERT eventually deployed its Bearcat, a military-style armored vehicle, which is typically used in barricade situations like the one that unfolded Tuesday.

The 17,550-pound wheeled vehicle can topple a wall, tear down a fence, resist small-arms rifle and transport 10 to 12 heavily armed officers to a volatile standoff or emergency situation.

Morando said the vehicle approached the house and officers inside told Wiemann to come out with his hands up.

“We believe he came out between the house and garage,” Morando said. “He had a scoped rifle in the driveway and took a defensive position. He raised the gun up to fire.”

According to the police report, “a (SERT) member fired at (Wiemann) striking the man.”

Police Capt. Steve Ignatz on Wednesday would not identify the officer. He also declined to say where Wiemann was struck, how many shots police fired and how many officers fired.

A Butler Eagle reporter nearby heard several shots fired about 3:45 p.m. A neighbor also reported hearing at least two shots.

Wiemann's rifle was loaded, police said, but he did not fire any shots. Police would not identify his rifle. They also would not say if there is any video recording of the shooting.

The state police major case unit is investigating what happened.

“A supervisor from another station is handling it,” Ignatz said.

Goldinger said his office is also involved. An assistant district attorney was at the scene Tuesday.

“We're going to have a county detective assist for transparency appearances,” he said. “We don't want anyone to second guess the investigation.”

He said that while he has “complete faith” in police investigators, “I think it's prudent to have an independent, second set of eyes.”

Along with the crime unit's probe, the department's Internal Affairs Division will conduct its own investigation, as it does in all shootings that involve troopers.

The findings of the separate investigations will eventually be turned over to Goldinger, who will ultimately determine if the shooting was justified or if criminal charges are warranted.

The troopers placed on administrative leave, in keeping with protocol, have not been formally interviewed, Ignatz said.

State police have a 72-hour waiting period before officers can give their accounts about what happened.

The waiting period, he noted, gives the troopers time to calm down from the traumatic event and undergo sufficient sleep cycles, thereby allowing for a keener and more accurate recollection.

A call to the Wiemann house Wednesday went unanswered.

Wiemann and his wife bought the house in May 1972, according to the county's recorder of deeds office.