Nairobi - A Kenyan court on Thursday sentenced four men to 40 years in jail each after finding them guilty of killing a prominent Scottish gemstone expert in August 2009.A crowd armed with clubs, spears, bows and arrows attacked and killed the geologist, Campbell Bridges, during a dispute over mining in a national park in the town of Voi, 170km north of the Kenyan port city of Mombasa.Bridges, a 71-year-old internationally-renowned gemmologist who had settled in Kenya in 1974, owned several gemstone mines in the Voi area. He was attacked as he drove his pick-up truck with his son and four other Kenyans.The accused, Mohamed Dadi Kokone aged 42, Alfred Makoko Njuruka aged 58, Samwel Machala aged 49 and James Chacha aged 56, had denied the charges in 2009 and were all out on bail except Kokone who failed to raise the cash bond."The accused acted unlawfully even if the deceased was rightly a trespasser, they had no right to take matters into their own hands. This type of jungle law has no place anywhere in a civilised society," Judge Moureen Odero, said as she delivered her ruling.Odero said witnesses had told the court during trial that tension had been brewing between the Bridges and local small-scale miners who accused the geologist of trespassing into their land."The locals who wanted to get a foothold into the mining industry viewed the deceased as an outsider who had been given a license to exploit the mineral wealth on their land," Odero said.Bridges is credited with discovering the green tsavorite gemstone in the late 1960s in the bushland on the border with neighbouring Tanzania, according to the New York-based International Coloured Gemstone Association.