The Bureau secured an order in the High Court for the home of 31-year-old Collopy in the village of Fedamore, Co Limerick.
Collopy bought the house a year-and-a-half ago in the village, nine miles east of Limerick city.
The house, described yesterday as reasonably large and comfortable, was purchased with cash for €150,000 in March 2002. It's estimated the property is now worth €250,000.
Gardaí believe Collopy moved back to his native home in St Mary's Park also known as the Island Field following the murder of crime boss Kieran Keane last January.
"We think he took over as the number one in the Keane gang after the killing," a CAB spokesperson said.
Neighbours yesterday said Brian Collopy was one of the most feared men on the Island Field.
"He's a tough guy, a heavy hitter, you wouldn't want to mess with him or you'd know about it," one neighbour said.
Gardaí confirmed Collopy has previous convictions for minor offences.
"They are nothing major and certainly not on the extraordinary end of the scale," a garda source said.
CAB has been working with the gardaí in Limerick for almost two years to clamp down on the city's notorious crime gangs.
The bureau is looking at all the assets of the gangs on both the north and the south side of the city. In the past they have been backed up by full time garda checkpoints in areas such as St Mary's Park.
"The gangs are being watched and we will continue to assist the Chief Superintendent in Limerick in the area of law enforcement," the CAB spokesperson said.
CAB was just about to move in on Kieran Keane before he was gunned down in Drombanna on January 29 last.
"We have looked at the assets of the drugs gangs in the Island Field. There was nothing of any value there because the properties were bought years ago," the CAB spokesperson said.
It's estimated the Keane gang own more than 30 properties in St Mary's Park.
The Keanes and the Collopys, though not related, have been traditional allies in St Mary's Park. They are involved in a bloody feud against the Ryans from the Kileely/Moyross area and the McCarthy Dundons from Ballinacurra Weston.
The feud has its origins in a dispute between Brian Collopy's father, Jack, and the late John Ryan.
Ryan, who was shot dead on July 7, assaulted Jack Collopy so badly that he was placed on a life support machine and suffered a mini-stroke. He has not been able to work since the incident.
The Keanes then became embroiled in their neighbour's row when John Ryan's brother Eddie tried to shoot Christy Keane but the gun jammed.
Shortly after this Kieran Keane murdered Eddie Ryan in the Moose Bar in November 2001.
It has also been alleged that two of Brian Collopy's brothers, Philip and Kieran, were the targets the night Kieran Keane was murdered.
Keane's nephew, Owen Treacy, who was stabbed 17 times that night, told the Central Criminal Court the gang who allegedly captured himself and his uncle wanted to lure the Collopys to a country road outside the city.
"We were told to sit there, play along and we would be okay," Mr Treacy said. He claimed the men wanted them to get Kieran and Philip Collopy "out the road for them" to kill them. "There was no way we could do that," Owen Treacy said.