Most of the 31 chimpanzees that escaped a sanctuary and attacked a group of sightseers in Sierra Leon two weeks ago have returned, but the leader of the group is still missing, said the sanctuary director on Saturday.
The April 23 attack on a taxi of American and Sierra Leonean tourists left the car's driver dead.
A Sierra Leonean man lost his hand in the mauling.
Head of the Tacugama chimp sanctuary outside of Freetown, Balasingam Amarasekeran, said 21 of the chimps had returned.
But 10 chimps, including the oldest and leader of the group, Bruno, were "still out on the hills".
Amarasekeran said the chimps had escaped at night, and had used sticks to disable a sliding metal door.
"We never thought they could use sticks to destroy the slide," said Amarasekeran. "We are dealing with a species that is very intelligent and which bypassed one of the safety mechanisms we put in place."
This is the first accident at the sanctuary since it opened 10 years ago.
The sanctuary has been closed to the public since the incident.
"We are very sorry for the loss of life. The whole incident was very unfortunate," said Amarasekeran.