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Luke Sparos leaves court on Monday.Credit:AAP

In his opening address at Sparos'NSW Supreme Court trial on Monday,prosecutor Craig Patrick SC said the 37-year-old was in custody awaiting a trial for cocaine-related offences when he began planning the killing.

Sparos had been one of a number of people charged through the same police operation and Mr Maika had become an"essential witness"in the case against the group,Mr Patrick told the court.

His desire to kill Mr Maika was motivated both by"retribution"and the desire to send a message,he said.

"He wanted to send a message to other witnesses about the risk of giving evidence against him,"Mr Patrick said.

Gemahl Maika was shot dead outside his home.

Mr Maika's murder was a crime involving a number of people,but it was Sparos who was"ultimately responsible"and just as liable as the man who shot Mr Maika,he said.

"Mr Sparos instigated and organised the killing of Mr Maika,using other people,"he said.

Mr Patrick said he expected the jury would hear evidence from the man who shot Mr Maika four times in the upper body and once in the head using a .44 calibre gun on April 6,2011.

The shooting occurred as Mr Maika returned to his Glen Alpine home and left him dead in the front yard.

The jury is also expected to hear evidence from another man who acted as a liaison between the shooter and Sparos'then brother-in-law,Mr Patrick said.

A man who passed Mr Maika's home address on to Sparos is also expected to provide evidence.

Sparos'trial before Justice Ian Harrison continues.

AAP