Qld referee's death 'cold-blood execution'

An accused murderer who was in love with a prostitute confessed to killing a Brisbane rugby league official after being duped by police posing as a fake criminal syndicate, a court has heard.

Tyson John Taylor, 41, has pleaded not guilty to murdering retired accountant Tony McGrath in May 2013.

He also pleaded not guilty to an attempted murder charge stemming from allegations he set Mr McGrath's home alight seven months earlier.

On the first day of his Supreme Court trial in Brisbane, crown prosecutor Vicki Loury told the jury Taylor shot the rugby league referee in a "cold-blooded execution" in his Woolloongabba garage.

The crown alleges Taylor was in love with a prostitute named Susan Stewart - a woman Mr McGrath believed he was engaged to - when he committed the crimes.

She said the jury would have "little difficulty" accepting he was guilty if they found a confession he later made to undercover police posing as a criminal gang was genuine.

Taylor had been recruited to the false syndicate after investigators exhausted their traditional methods, taking on pretend jobs such as surveillance work and collecting fake diamonds, Ms Loury said.

This culminated in February 2014 when he met with its "big boss" in a penthouse hotel suite, the court was told.

The jury heard Taylor initially denied involvement in Mr McGrath's death but eventually said he shot him in the head after the covert officer emphasised the organisation's values of truth, respect and honesty.

Photographs of Mr McGrath's body lying next to a large pool of blood sprawling on his garage floor were also shown in the court.

It came after Mr McGrath's sister, Carmel Waugh, gave evidence her brother had been in love with Ms Stewart and wanted the relationship to work.

The jury also heard Mr McGrath had given Ms Stewart more than $550,000 before he died.

The crown alleges Ms Stewart secretly manipulated both men out of greed and thought she was going to inherit Mr McGrath's estate.

Ms Loury said an analysis of Ms Stewart's finances showed a total of $1.1 million had been transferred to her by three different men between July 2009 and May 2013.

Taylor was also a client of Ms Stewart with invoices found at her house suggesting he'd spent more than $20,000 on sexual services between August 2008 and February 2009, she added.

The trial, which continues before Justice Martin Burns, is expected to run for three weeks.