British gunshot residue expert Angela Shaw took to the stand as a witness in the double murder trial of Ricco Furbert and Haile Outerbridge.

The forensic scientist Angela Shaw, who has given evidence in “30 to 40” cases involving gunshot residue, said she was unable to determine whether a gunshot residue particle found on defendant Le-Veck Roberts originated from a firearm discharge.

Christoph Duerr, 26, from Sandys, and Mr Roberts, 21, from Warwick, were charged with two counts of premeditated murder in connection to the fatal shooting of the men inside Belvin’s Variety on January 23, 2013.

Mr Roberts is facing a separate charge of attempting to kill Zico Majors on January 16, 2013 in the Khyber Heights area of Warwick although Mr Majors said Mr Roberts was not the one who shot him. He was also charged with taking a vehicle without consent and taking a vehicle without lawful authority.

Ms Shaw said another report on Mr Roberts showed samples taken two days after the incident, containing true gunshot residue but said they could have come from any source. She explained that gunshot residue will only remain on a person for a maximum of four hours.

The question was put to Ms Shaw by defence lawyer Charles Richardson whether a person could be contaminated with gunshot residue when coming into contact with a police officer, for example when they are being arrested, having their pockets checked or put in to handcuffs. She said there was no way to tell whether residue came straight from a gun or whether it has been transferred.

Ms Shaw conducted two surveys in Bermuda in areas police officers frequent, including Hamilton Police Station where one true gunshot residue particle was found and a number of one and two component particles of lead and antimony were found. The second study was at LF Wade Airport where several one and two component particles were found but no true gunshot particles. She said the survey shows the prevalence of particles in the environment and how they can be picked up by a person.

Cross examined by prosecutor Carrington Mahoney, the witness accepted that while there are other potential sources for the particles found on Mr Roberts’s hands, such as fireworks and brake pad linings, the presence of other elements, such as magnesium, typically distinguish them from particles produced by the discharge of a weapon.

She also told the court that while GSR particles are usually lost from hands after a period of hours, she could not rule out the possibility that the particles could be transferred back onto the hands some time later if a gunman handles the firearm or the clothing they had been wearing.

“It could account for the transfer of particles, but I wouldn’t expect to see just one or two component particles,” she said.

She further accepted that she was unaware of all of the evidence in the case, such as that Mr Roberts was wearing a ballistics vest at the time of his arrest.

She subsequently accepted that there was nothing in the evidence before her to indicate that the particles did not come from the discharge of a firearm.