It was just after 8.50am on August 29, 2014, and Diego Carbone had been stopped by customs officers at Sydney International Airport.

The officers phoned Stephen Hunt, a NSW Police detective from the Homicide Squad, who soon arrived and was escorted through.

He approached Mr Carbone and showed his badge.

"Diego, you're under arrest for the murder of Bradley Dillon," Detective Sergeant Hunt said.

Mr Dillon, 23, was brutally murdered in Leichhardt 18 days earlier.

He collapsed on the footpath after he was stabbed four times in the back and shot three times, in what the Crown alleges was an "ambush" at an underground car park.

Mr Carbone is on trial for the murder, with the Crown alleging he was part of a joint criminal enterprise with his cousin, Antonio Bagnato, to kill Mr Dillon over a $2000 debt.

Det Sgt Hunt gave evidence on Wednesday as the trial opened.

Darlinghurst Supreme Court heard Det Sgt Hunt, the officer in charge of the homicide investigation, was "certain" Mr Carbone was his man.

"The accused said 'yes, are you sure you have the right guy?'," Det Sgt Hunt said, reading from a statement tendered to the court.

"I said 'quite certain, and we're going to take you to Mascot Police Station'."

Det Sgt Hunt said he noticed "a number of small injuries" on the side of Mr Carbone's face, which were covered with scabs and appeared to be healing.

Photographs were later taken of the injuries and a tattoo on Mr Carbone's back, of the biblical figure Saint Michael.

The Crown alleges the tattoo is a reference to the Saint Michael Fight Club, a boxing and mixed martial arts club linking Mr Dillon, Mr Carbone and Mr Bagnato.

A second witness, Amelie Louise, told the court she was walking near Leichhardt TAB at about 5.30pm on August 11 when she heard two voices involved in a "very aggressive" argument.

"I could hear one man mumbling, and he sounded very feeble and scared," she said.

"There was another person with a very, very violent voice. I've never heard anything as scary as this voice before, and I've grown up around violence.

"All I could hear were swear words. It sounded like he was asking for something.

"I heard 'f---' a lot. Maybe three to four times."

The jury of six men and six women will be taken to Leichhardt on Thursday morning to examine the scene where Mr Dillon died.

The trial continues before Acting Justice Jane Mathews.