Nathaniel Train died in a shootout with police reinforcements alongside his brother Gareth and wife Stacey at the remote scene, sources have confirmed to AAP.
All three are considered to be offenders actively involved in the ambush.
NSW police last week launched an appeal for public assistance to locate 46-year-old Nathaniel Train, last seen at his residence in Dubbo on December 16, 2021.
While his whereabouts were unknown, it was believed Train, a former schoolteacher, had remained in touch with his family until early October.
He was then reported missing after apparently falling out of contact, with local police commencing inquiries on December 4.
"Police and family hold serious concerns for Nathaniel's welfare," according to the appeal notice issued last Wednesday.
Train was described as being of Aboriginal/Torres Strait Islander appearance, about 183cm tall, with a thin build and a long, grey beard.
He was last seen wearing a white shirt and jeans and was known to always wear brown boots.
Police sources have confirmed Train was one of the gunmen later shot dead by police at Wains Road in Wieambilla on Monday night.
Earlier in the day, he and his brother Gareth allegedly gunned down police constables Matthew Arnold, 26, and Rachel McCrow, 29 who were there apparently in search of Train.
A neighbour, 58, who went to the scene following the disturbance, was also fatally shot.
Local media reports indicate Gareth and Stacey Train owned the property.
According to News Corp Australia, Nathaniel Train had previously worked as a primary school principal at Walgett and had at one time taught in Queensland.
"We got a request from NSW that a person had been missing for a considerable period of time and then that request was given to the local police to go to this address to check on that missing person," Police Commissioner Katarina Carroll said on Tuesday morning.
"I understand from my brief that that person had been missing from up to about 12 months but people had been in contact with him.
"However, that contact was lost in recent days and they just wanted to check on that missing person."
