Nine suspects are now being held over the killing of British helicopter pilot Roger Gower who was on an anti-poaching mission, police in Tanzania say.
Seven more suspects have been arrested for the shooting of Mr Gower, who was on a joint operation with Tanzanian wildlife authorities when he was shot, Simiyu regional police commander Lazaro Mambosasa said.
Mr Gower died on January 29 in Maswa wildlife reserve, near Serengeti National Park.
Mambosasa said some of the suspects identified the man who pulled the trigger. Three elephant tusks and 29 firearms were seized in the operation to arrest Mr Gower's killers.
Tanzania has been identified as a key hotspot for elephant poachers.