A total of five people have been arrested in connection with the killing of British helicopter pilot Roger Gower who was shot dead by elephant poachers in Tanzania.
A suspected gunman and accomplices plus members of a network providing illegal weapons and smuggling ivory are among those who have been arrested, according to the Friedkin Conservation Fund.
The Texas-based Friedkin group, which operates in Tanzania, suggested that more arrests could follow.
Mr Gower, 37, was helping authorities in the African country track the criminals when they fired on his aircraft on January 29.
He managed to bring the helicopter down in the Maswa Game Reserve, near Serengeti National Park in the north of the country, but died from his wounds before he could be rescued.
Tanzania is fighting a bitter struggle to stop ivory poachers - a report last year stated 60% of its elephant population had been lost in the previous five years.
China is the world's largest market for illegal ivory, which has been thriving under the cover of legal ivory sales. Tanzania also last year charged a Chinese woman, Yang Feng Clan, 66, with smuggling 1.9 tons of ivory from the country between 2000 and 2014.
Mr Gower qualified as a pilot in 2004 and moved to Africa around two years later, according to a profile with his former employer Tropic Air Kenya.
Mr Gower's brother Max said he was proud of him and how he had managed to land the helicopter and allow his passenger, a friend and colleague, to get out.
He said that his sibling did not want to sit behind a desk, and quit as an accountant the day he qualified so he could go to work with the two things he enjoyed the most, flying and animals.
Dan Friedkin, the Friedkin Conservation Fund chairman, said in a statement: "We are confident that the Tanzanian authorities will investigate and prosecute those involved to the absolute full extent of the law.
"By bringing these individuals to justice, it will honour Roger's memory. We also fervently hope that it will mark the turning point in Tanzania in the fight to protect elephants and our wildlife heritage."