A jury has been shown a picture of a knife allegedly used to stab teenager Kayden Moy on a beach in North Ayrshire last year.
Kayden, 16, from East Kilbride, South Lanarkshire, died following the incident in Irvine on May 17.
Cole Turley, 18, has since admitted murdering him.
Jay Stewart, 18, and a 15-year-old boy who cannot be named for legal reasons are on trial at the High Court in Glasgow accused of murdering Kayden while acting along with Turley.
On Monday, the court was shown a picture of a weapon allegedly used in the murder, which is described as a “brown lock-back knife” and features a metal blade with three holes close to one edge, attached to a brown handle.
Giving evidence via video-link, forensic biologist Claire Vallance said blood and “greasy material” from Kayden Moy had been found on the weapon’s blade.
She said blood belonging to Turley was also found on the handle.
She also said small amounts DNA from “three other individuals” was found on the weapon’s handle, but that there was not enough of this to trace it to specific people.
She told the court that analysis showed the knife previously had more blood on it, but that evidence demonstrated the “entirety” of the weapon had been cleaned.
“In our opinion, more blood had been present on the knife but had been removed by wiping and/or washing,” she told the court.
Ms Vallance also gave evidence about DNA found on clothing and other items allegedly associated with Kayden’s death.
These included a 53cm-long retractable metal baton, which she said was found to have blood spots and “contact bloodstains” attributable to Stewart.
She also told the court a “small amount” of Stewart’s DNA had been found on a black-handled knife, which was recovered from the freezer of the East Kilbride property.
However, she said since no blood was found on the blade, “we are unable to ascertain if the knife was used to injure anyone”.
Cross-examining the witness, Stewart’s lawyer Donald Findlay KC put it to her that when someone’s DNA is found on an item, it does not say anything about how it got there or how long it has been there for.
“The fact is DNA may tell (us) there is DNA there, but we have to be very careful and not jump to conclusions about either the circumstances in which it was transferred, or the timescale in which it was deposited,” he said.
Turning to the description of the lock-back knife in Ms Vallance’s report, Mr Findlay said: “It may well be that the jury have little difficulty in concluding that the brown-handled lock-back knife was in fact the murder weapon, given Cole Turley pled guilty to the crime of murder.”
He put it to her the fact his client’s DNA was not found on the weapon is “consistent with Jay Stewart never having held that knife in any way”.
He also suggested to her that since analysis cannot show how long DNA has been on an object, she cannot say when his client’s DNA got onto either the baton or the clothing.
“It is possible it was from some period of time prior to the the day of Kayden Moy’s death?” he asked her.
She replied: “It could be.”
The court was later shown CCTV footage and mobile phone videos from East Kilbride and Irvine on the day of the fatal incident.
Some of the footage showed Turley, Stewart and the 15-year-old boarding a train to Irvine.
Prosecutor Liam Ewing KC showed the court mobile phone footage which was recorded by others on the beach on the day of the incident, suggesting one clip showed that Kayden fell down and then was struck.
He showed the court CCTV footage of Turley, Stewart and the 15-year-old running through Irvine after the incident, suggesting that part of it showed a “handshake” between Turley and Stewart.
Mr Findlay cross-examined detective constable Brian Hamilton, who compiled the CCTV footage.
The KC said the “handshake” appeared to have been initiated by Turley.
It is alleged that while acting with Turley, Stewart and the 15-year-old pursued Kayden, causing him to fall to the ground and repeatedly stabbed him on the body with a knife, leaving him so badly injured that he died.
Stewart and the 15-year-old deny all charges against them and have lodged special defences of incrimination.
The two boys face a number of other charges, including that Stewart is accused of having a baton and a knife or similar instrument and the 15-year-old of having a knife on May 17 last year.
They are also accused of challenging others to fight and brandishing knives and a baton or similar instruments at Irvine beach on May 17 last year.
It is also alleged they “culpably and recklessly” threw rocks at members of the public there, placing them in danger of injury.
They are also accused of attempting to pervert the course of justice between May 17 and 21 in Irvine, East Kilbride and elsewhere in a number of ways.
Stewart is also accused of sending threatening messages to Jay Mooney, 18, on social media in May last year.
The trial continues before Judge Lord Scott.
