Only one of numerous swabs purported to have been taken from the hands of three men after they were shot and killed during an alleged shoot-out with police on January 12, 2013 tested positive for nitrate, which is a key element of gunpowder, a seven-member jury heard on Wednesday.

This testimony came from a retired government forensic analyst who tested swab samples for evidence of gunpowder in the case.

Six members of the Jamaica Constabulary Force are on trial in the Home Circuit Court in Kingston for murder in relation to that 2013 incident on Acadia Drive in St Andrew, which led to the demise of Matthew Lee, Ucliffe Dyer, and Mark Allen.

It was alleged that cops were on operation when they signalled to the driver of a blue Mitsubishi Outlander motor vehicle to stop. It was further alleged that the driver was initially hesitant to comply, but when the vehicle stopped, men alighted from it to engage the police in a gun battle, during which they were killed.

Two illegal firearms — a Mac 11 sub-machine gun and an Arcus pistol — were reportedly taken from the deceased men. A fourth man was said to have escaped.

The retired lab analyst told the court that the hands of Lee, Dyer, and an unidentified male were swabbed, but only one bore a positive result for a trace of nitrate. Two T-shirts purported to belong to Lee and another of the deceased were tested for evidence of gunpowder as well, but no confirmation was made.

However, despite the presence of nitrate on one of the samples, the expert said gunpowder was not determined to be the cause.

“Nitrate can be found in the environment, in soil, fertiliser, and matches,” she said, before explaining that it is possible for a person to have nitrate on his or her hand and clothing if they fall to the ground and interact with soil.

She explained that key ingredients of gunpowder are nitrate, lead, antimony, and barium.

Lead, barium, and antimony, were not found following tests.

Previously in the trial, a witness who was the detective constable who collected much of the evidence at the scene of the shooting, said that he did not conduct any swabs for gunpowder, explaining that another detective carried out that function.

However, based on his knowledge, he said that there are certain factors such as movement that could affect the placement of gunpowder. Other factors which he highlighted were weather and type of garment being worn by a person firing a gun.

The witness on Wednesday added that when swabs are taken for the purposes of being tested for presence of gunpowder, it is almost automatic for it to be done to the palms and back of hands. In cases in which clothing exists, the garments would be tested for gunpowder residue as well.

She said that when a firearm is fired, the components of ammunition undergo changes and explosion. The components of the ammunition are burnt, some fully and some partially. She added that gases are formed and these gases, when they come under pressure, seek to escape, and so it escapes through the muzzle of the firearm.

“These particles are called gunshot residue. When someone fires and the residue exists, some travel with the bullet while some is blown backwards and become deposited on anything in its path.”

Prosecutor Kathy-Ann Pyke is the lead prosecutor in the trial.

On trial for murder are Sergeant Simroy Mott, Corporal Donovan Fullerton, and constables Andrew Smith, Sheldon Richards, Orandy Rose, and Richard Lynch. Corporal Fullerton is also charged with making a false statement to the Independent Commission of Investigations.

Attorneys representing the cops are Hugh Wildman, John Jacobs, and Althea Grant-Coppin.

Justice Sonia Bertram-Linton is the presiding judge in the matter.

The trial resumes today.