A charity says five people have been arrested in total over the death of British helicopter pilot Roger Gower, who was shot down by elephant poachers in Tanzania.
According to the Friedkin Conservation Fund, those arrested included a suspected gunman and accomplices, along with members of a network channeling illegal weapons and smuggling ivory.
The Texas-based group, which operates in Tanzania, also suggested that more arrests may follow.
Mr Gower, 37, was helping authorities in the country track the criminals when his aircraft was fired upon last month.
He brought the helicopter down in a game reserve near the Serengeti National Park but died from his injuries before rescuers were able to get to him.
Mr Gower, previously an accountant in London, qualified as a pilot in 2004 and moved to Africa around two years later - aiding Tanzania's struggle against illegal ivory.
The country last year charged a Chinese woman, Yang Feng Clan, 66, with smuggling 1.9 tons of ivory from the country between 2000 and 2014.