Kenyan police have arrested the suspected mastermind in the killing of a Scottish-born geologist, who was attacked last week by men armed with arrows, spears and machetes in an apparent dispute over mining rights.

Alfred Makogo Njiruka, the chairman of a small miners association, was arrested Wednesday in Taveta, some 225 miles from the capital, Nairobi.

"We believe he is the mastermind behind the killing," the area's police chief, Herbert Khaemba, said Thursday. Police were still searching for other suspects.

About a dozen people attacked 72-year-old Campbell Bridges last week after he stopped to remove a log blocking a road, police said. Bridges had been driving to a mining camp by Tsavo West National Park, near where he lived.

In the 1960s, Bridges discovered a rare green variety of garnet, first in modern-day Zimbabwe and later in Kenya's neighbor Tanzania. Today it is mined chiefly in Tanzania and Kenya, and is named tsavorite after the park.

Bridges had received threats from people disputing his right to use a mining permit in the area, police said. Bridges had been mining for gemstones in the vicinity of Tsavo since the early 1970s.

Southeast Kenya is sparsely populated and impoverished, because its dry, low-lying land is poor for most crops. The area's gemstone riches are mined by handful of companies. Many locals eke out their livings on plantations growing sisal, a plant that produces stiff fibers for making rope.