Thomas Mair was armed with British-made hollow-point rifle bullets more commonly used to kill vermin when he murdered MP Jo Cox, his trial heard.A plastic bag found in a holdall when the alleged killer, 53, was arrested was found to contain 25 live .22 calibre rounds, jurors were told.Twelve of the rounds were lead hollow-point cartridges made by British maker Eley, firearms expert Andre Horne told the Old Bailey trial. The other 13 were made by a German firm. A gun that was presented in evidence during the trial of Thomas Mair Credit:West Yorkshire Police A photograph of the gun in a bag next to a small drop of blood Credit:West Yorkshire Police Mr Horne said hollow-points were designed to expand after firing, adding: “The idea of that is to cause a greater wound size, especially when hunting, which would be considered a more humane way of disposing of animals.”He explained this was because a bullet staying together and causing a smaller wound might allow it to escape, prolonging its suffering before it died.He added: “They are most commonly used for hunting vermin, squirrels, rabbits and other small animals.”Mr Horne said that the bullets could be legally owned in the UK with the correct firearms licence. Show more Prosecutor Richard Whittam QC said to the expert: “In its long form it’s a firearm and you could have had lawful possession of it with a certificate. But in its reduced size it is a banned weapon in this country altogether?”Mr Horne replied: “That’s correct, yes.”Kerry Versfeld, of the National Ballistics Intelligence Service, examined the gun, two casings, a spent cartridge and items recovered from the post mortem. Blood stains that were a “billion-to-one” match to both Mrs Cox and Mair were found on the gun and dagger when they were tested, the court heard.Jurors also heard that Mrs Cox tried to shield her face with her hands as her killer shot her in the head.They were shown the modified .22 calibre Weihrauch rifle found in the holdall. The bolt-action gun had had its shoulder stock and all but 4cm of its barrel removed, Mr Horne said.This, jurors heard, would have made the now 29cm (12-inch) weapon fireable with one hand, but decreased the penetrating power of the resulting shot – perhaps accounting for why the two shots to Mrs Cox’s head failed to penetrate her skull. A knife that was allegedly used in the killing of Jo Cox Credit: West Yorkshire Police Testing “conclusively” determined that two cases from the scene and one found in nearby John Nelson Close were all fired by the rifle, she said.Two bullets recovered were “consistent” with being fired by the gun, she told jurors.The court was also shown the dagger allegedly used to stab Mrs Cox 15 times in the chest and abdomen.Mr Horne said it was a Fairbairn-Sykes “fighting dagger”, a design first made in 1941 for British special forces and commando units, with a 17.4cm blade.But he added: “It was determined that it was a fake replica and not one that was produced for the military.”The trial continues. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.