Gunshot residue discovered on the hand of an accused killer may have come from another source, the Supreme Court heard yesterday.

Christoph Duerr, 26, from Sandys, and Le-Veck Roberts, 21, from Warwick, have both been charged with the premeditated murders of Haile Outerbridge and Ricco Furbert, who were shot dead inside Belvin’s Variety on January 23, 2013.

Mr Roberts is also further charged with attempting to kill Zico Majors on January 16, 2013, in the Khyber Heights area of Warwick; taking a vehicle without consent on the same day; and taking a vehicle without lawful authority on the day of the murders.

Prosecutors allege that Mr Roberts was the gunman in both shootings, while Mr Duerr is accused of storing and supplying the weapon used.

CCTV footage of the shooting, shown to the jury this week, showed a man wearing blue clothes and a black full-face helmet chasing Mr Furbert to a store room near the rear of the shop and opening fire. Mr Roberts was arrested by armed officers on January 25, 2013, after Police received reports that a vehicle linked to the incident was on the property. Gunshot residue (GSR) swabs of Mr Robert’s hands on the day of his arrest revealed a single particle of GSR on the back of his left hand along with several particles commonly associated with the discharge of a firearm.

Expert Allison Murtha told the court that true GSR contains three elements — lead, barium and antimony — which are released in a plume when a firearm is discharged. While particles containing one or two of the components can come from either a firearm or another source, such as brake-pad lining, particles containing all three are almost certainly the result of a gunshot.

She explained that the presence of GSR on a person means they either discharged a firearm, were near someone when they discharged a firearm or have been in contact with someone or something that had.

Continuing on the stand, Mrs Murtha also discussed the testing results of a blue jacket recovered from Mr Roberts’s home.

The jacket was found to contain several single component particles, and a pair of two-component particles were found on the jacket’s right sleeve.

A grey jacket was also tested and found to contain a single two-component particle along with a host of single-component particles. She also testified that she tested several other items in connection to this case, including two helmets and a black mask, which was associated with Gariko Benjamin.

The mask was found to contain three particles of true GSR along with eight two-component particles. Both of the helmets were found to have a host of single-component particles, while one was found to have four two-component particles.

Swabs of Mr Benjamin’s hands, meanwhile, showed a single particle of true GSR, several two-component particles and more than 80 single-component particles.

Under cross examination by Charles Richardson, representing Mr Roberts, Mrs Murtha accepted that she did not know how “control” samples were taken, stating that different police services have different policies. While some swab the general area, others keep the swab sealed to test if the swabs themselves are contaminated.

She also agreed that the optimal time to collect samples for GSR testing is within six to eight hours of the firearm being discharged, noting that particles are lost over time. Mr Richardson also questioned the witness about a study carried out in Bermuda in 2014 in which a single particle of GSR was found on a chair in the Hamilton Police Station, while single-component particles were found on a Bermuda Police Service armed response vehicle and on chairs in the Bermuda Police Service’s social club.

Mrs Murtha also said that it would be possible for an armed officer to transfer GSR on to a suspect while arresting them, provided that they have particles on them.

During re-examination, prosecutor Carrington Mahoney asked if it was possible that GSR could be transferred from an officer three months after they last discharged a firearm, particularly if the officer was wearing entirely different clothing.

She responded: “Transfer still could be possible, but the possibility is much less likely in that scenario than if they had discharged the firearm less than three months previously.”