Byrne had a history of fraud and counterfeiting. In November 2002, he agreed to repay
€43,353 in unemployment assistance that he was not entitled to. He paid the
Revenue Commissioners €208,400 after Revenue and the
Criminal Assets Bureau issued his wife and him with a tax assessment of €378,612 in 2004. Some of the assessment was paid from €22,000 in cash seized at his home in 2001. He had been a friend of
Gerard Hutch and was photographed with him in
Lanzarote in 2014. After the
fatal shooting of his son David he and Hutch fell out. As a result of the
Kinahan-Hutch feud, Gerard Hutch met with
Jonathan Dowdall and the
New IRA with a view to the latter group acting as mediators between the two gangs. Hutch told Dowdall that Byrne would need to be consulted and "on board" before a ceasefire could be negotiated. In 2018
High Court found that Byrne, his wife, his daughter Maria and three others "while not members of the Byrne organised crime group, are closely related to its members and involved in money laundering" and "They also have access to the proceeds of criminal activity carried out by the Byrne organised crime group". Both Byrne and his wife attended the trials of Gerard Hutch and Jonathan Dowdall for the shooting of David Byrne. The
Special Criminal Court found Hutch not guilty and the Dowdall trial collapsed after the death of the lead investigator. ==Personal life and death==