A US crime scene expert was grilled over her techniques by a lawyer for one of two men accused of murdering Aquil Richardson.

Janice Johnson, who runs a Florida business called Forensic Pieces, examined clothes seized from the homes of Antoine Anderson, 31, and Philip Bradshaw, 26, during the Police investigation.

She also examined bullet cases and spent slugs as part of the probe.

Ms Johnson told Supreme Court on Monday that she checked the garments for blood, gunshot residue and DNA evidence of who might have worn them.

Ms Johnson has not shared the results with the jury, explaining that she passed her findings on to other experts in the US for further tests.

However, Senior Crown counsel Carrington Mahoney told the jury during his opening speech on January 26 that investigators found gunshot residue on a jacket worn by Bradshaw that night, and on a pair of pants belonging to Anderson.

According to prosecutors, the accused men arrived on a motorbike at the murder scene in Camp Hill, Southampton, on the night of Boxing Day 2007.

Bradshaw is said to have been the pillion passenger, wearing a jacket with a fur-trimmed hood that he'd borrowed from family friend Malika Gumbs.

According to witnesses at the scene, the pillion passenger shot at a group of men which included Aquil Richardson and Lavar Smith before dismounting and shooting Mr. Richardson twice in the head while he was on the ground.

The men are jointly charged with murdering Mr. Richardson and wounding Mr. Smith in the leg under the principle of joint enterprise.

That means if one assisted the other in the crime, they are both equally guilty. They have pleaded not guilty to both charges.

On Monday, Ms Johnson explained how she tested clothing items including the jacket and pants in question, and a ski mask and eye mask found at Anderson's home.

She swabbed suspected blood stains on some of the garments and used a sticky stub on each one to pick up any gunshot residue before sending the swabs and stubs off for further analysis.

Cross-examining her over this yesterday, Benjamin Nolan QC, representing Anderson, asked how she ensured her laboratory tests for gunshot residue were not contaminated by outside material.

"Are any firearms users ever allowed in (to the lab) and what particular steps do you take to stop them?" he inquired.

Ms Johnson said Candy Zuleger, who runs the lab, would be able to speak to that.

However, she added: "I don't have a firearm or use a firearm. The area I work in is used solely by me."

The lawyer responded: "I'm not suggesting that you come to work with a firearm, but is the laboratory used for examining firearms?"

She replied: "No, it's a DNA laboratory... we don't discharge firearms in the laboratory."

Pressed again over whether firearms are examined in the lab, Ms Johnson said Ms Zuleger would have to be asked about that, but explained that she did not examine any firearm in the current case, only bullet cases.

"In the same place that the suspect garments were examined?" asked Mr. Nolan.

Ms Johnson agreed this was the case, but stressed that her work area was cleaned between tests on the bullet cases and the garments.

"Before you begin an examination of a suspect item, is there what I call a quality-control check on the laboratory itself the surfaces to ensure it's sterile for gunshot residue?" inquired the defence lawyer.

Ms Johnson replied: "I sanitise the area... and I'm wearing gloves, and when I sanitise the area I remove those gloves and put down fresh butcher paper and examine one item of evidence at a time unless it's packaged together."

The case continues.